# Workshop Design



## kingcod (16 Feb 2011)

I'm in the early stages of building my workshop. Its going to be 7 x 3.5 m on a concrete raft using lots of inspiration from this site, not least the blockwork and timber design here.





(the coloured blocks are the odd sized ones I need to cut!)

I have a few of questions before I go much further:


*1. The concrete base*
Q: Is reinforcing with steel bar worth doing or will my 100mm concrete on compacted subbase be enough?

Laying the electric cable into the building I would like it to be set in through the concrete base. 
Q: Do I need to cut through the damp proof membrance to allow this to happen? won't this compromise the DPM?
Q: How far in should the conduit for the cable appear? I am guessing the width of my block wall plus cladding plus a bit more?

2. For the roof of the timber frame I have got so far and got stuck in finishing the design of the gable end (red denotes the pieces I am referring to):





Uploaded with ImageShack.us

I have a nice support for the ridge board, but cant see how to get a rafters up each side to the end of the top plate. I am aiming for an overhanging rake but the vertical support just seems to get in the way of acheiving this. Do I butt rafters to the vertical pieces to end up flush with the gable end? It doesn't look such a good idea. I am almost wondering whether to do a complete redesign around ply gussets like this but I like the idea of a ridge board that rafters adhere to. am not sure how a ridge would fit to the ply gussets build.

Any help and advice gratefully received!


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## OPJ (16 Feb 2011)

Instead of having that support piece at the end, you could try temporarily bracing two rafters together (at the correct angle; allowing for the thickness of the ridge board at the top) and then lift the assembly in to position before fixing to the wall plates. Do this at either end and you can then drop the ridge board in between the two (you may also want to fit a temporary support to prevent it from dropping). Depending on the length, you may need to repeat the same again with another frame near the centre of the ridge, to prevent it from sagging(?).

From there, you could be able to set out the centres for each intermediate rafter, do you seat and plumb cuts and nail them in to place, one at a time. It's actually easier than how I've probably made it sound!


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## monkeybiter (16 Feb 2011)

With regard to the base, my workshop is of a similar size, but fully blocked double skin walls up to a tiled roof, and the base is approx. 4"-5" thick with 6"-8" around the edges, all on top of sledgehammered rubble.
No rebar, no cracks, after more than 10 years. Maybe it's luck ?


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## Dibs-h (16 Feb 2011)

kingcod":5uz7qpfu said:


> I'm in the early stages of building my workshop. Its going to be 7 x 3.5 m on a concrete raft using lots of inspiration from this site, not least the blockwork and timber design here.
> 
> 
> 
> ...



Cable access - yes you would have to puncture the DPM, but why can't you wrap extra DPM around the pipe and join it to the main sheet of DPM, with some of the Butyl-like joining compound (that appears sepcially made to do that)? As for where - depends on where you want your distribution board and whether you'd want the cable to effectively come up inside the timber walls or not in the walls?

Gable ladder - that's what they call it, the overhang. To achieve this - the ridge board needs to overhang the outer end wall (which you have), as do the wall plates (which you don't), and then you treat it as just another set of rafters (slight simplification - but that's it in essence). Have a look at the following webpage and the 1st picture - a picture speaks a 1000 words and all that,

http://www.askthebuilder.com/578_Roof_F ... sics.shtml

Slab - personally I would reinforce it - marginal extra cost, but it allows you to increase the loading on it and should there ever be any settlement or voids, it'll span those with no issues.

HIH

Dibs


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## Deejay (16 Feb 2011)

Hello

_Laying the electric cable into the building I would like it to be set in through the concrete base. 
Q: Do I need to cut through the damp proof membrance to allow this to happen? won't this compromise the DPM?_

If it was my building, I would prefer not to perforate the damp proof membrane. I assume that you will feed the power through a SWA cable, which is not easy to bend (minimum bending radius six to eight times the diameter of the cable).

I would suggest that you clip the cable to the outside of a wall , terminate the SWA in a box and fit the consumer unit right behind it on the inside. If you leave long tails on the wires in the SWA they can be fed through a horizontal conduit from the back of the box straight into the back of the CU.

EDIT

*If you want the CU somewhere else, connect twin and earth to the SWA in the external box , run that through the wall and take it to the CU.*


This has caused a few comments later in the thread. Paul wrote ...

As I was asked to back up my comments earlier with regard to the electrical installation then IF you want a BS7671 Reg. No. as to why you should not fit an external joint box to go from SWA to T&E in your sub main, try 132.7, 133.3, 134.1, 510.1, 510.2, 512.2, 513.1, 521.1, 522 (group), 526.1, 543 (some of this group),.
You would also need to refer to reg 422.3 when undertaking your internal install.

Paul is a registered NICEIC contractor, so you'd be wiser to take his advice, rather than mine.

At the end of the day you (KC) are using a spark, who will issue the Part P certificate, so let him decide.



Cheers

Dave


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## Rob Platt (17 Feb 2011)

Extend your ridge beyond the gable and support, fix rafters then cut off excess. What`s your roof covering. You have no collars I think you may well get spread at that length. I would think a dog leg raft would be better. Electric cable should be ducted. Put in duct and seal around.
All the best
Rob


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## Mcluma (17 Feb 2011)

Deejay":138esaeo said:


> Hello
> 
> _Laying the electric cable into the building I would like it to be set in through the concrete base.
> Q: Do I need to cut through the damp proof membrance to allow this to happen? won't this compromise the DPM?_
> ...




That is how I have done it on my cabin build


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## kingcod (26 Feb 2011)

Thanks for the advice so far. I will stay clear of compromising the DPM by bringing electrics up to ground height outside the buidling and then fitting as you suggest Dave.

Olly I have gone with your suggestion to dispense with the permanent end support. It is looking neater.

Dibs I have shown a ladder gable of sorts

Some measurements to show the size of the thing.





Am I overdoing it with rafters spaced at 400 centres?

Roofing material probably something like OSB and Onduline or felt tiles. I don't think I can afford cedar shakes. Which takes me to the weight of it and potential spread ...

Rob I am not sure the most economical way to prevent spread ... so a couple of options shown - one for a collar (in yellow) set in the top third of the roof, secured with ply, and the other (in red) uses lengthier timbers resting on the top plate - I guess these would be called ceiling joists though they are to do the same job. Would one be better than the other? I know one would cost more!


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## monkeybiter (26 Feb 2011)

I specifically didn't want crosspieces when I built mine, so I bought a length [~20'] of steel 'I' beam [9" web] which is supported at either end at ridge height, the rafters are supported on the walls and on the ridge, tied together across the ridge. There are no cross pieces to get in the way overhead, and no tendency to spread as the direction of the force on the wall top from the rafter is vertical.


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## Deejay (27 Feb 2011)

Morning KC

You might find this thread useful ...

post460872.html?hilit=shed#p460872

The author, Mike Garnham, no longer contributes to this forum, but does so on The Wood Haven. 

Have a look at ...

http://thewoodhaven.co.uk/phpBB3/viewto ... hilit=shed

When you get round to cutting the roof, have a look at ...

http://www.blocklayer.com/

Cheers

Dave


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## Rob Platt (27 Feb 2011)

Red is better than yellow because you can spike it directly into the stud heads. But yellow maybe enough if? as follows I cant see any sizes other than 400c/c so whether its overkill or not? i cant see your location. Wind and snow loadings and worse case scenarios should be considered in the roof design and construction. If you put a chunk of steel into the ridge you will have to factor that into the calculations especially as its over a doorway.
All the best
Rob


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## NetBlindPaul (27 Feb 2011)

I would NOT put a "joint box" on the exterior of the building guys!
By all means take the SWA up the exterior of the building, I would take it up to soffit level and into the building intact then run the SWA to the point where you are going to locate the consumer unit.
How you joint up from there depends on your exact configuration.
Please also remember that the wiring comes under building regulations part p unless you get someone registered with a part p competent persons scheme to undertake the installation.
There are also a few other things to consider when installing electrical systems exterior to the building in which the supply originates, please remember electricity kills!


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## Deejay (27 Feb 2011)

Evening Paul

_'I would NOT put a "joint box" on the exterior of the building guys!'_

Is there any reason why this should not be done?

Would it contravene any of the reg's, assuming that a box with the appropriate IP rating was used?

Mcluma and I are probably not the only people who have done this, and I would like to know if it is 'legal'.

Cheers

Dave


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## NetBlindPaul (27 Feb 2011)

Why add an additional joint into the cable?
IF you use a screwed joint, such as a "chocolate block" this has to be accessible for inspection. (Regs)
You are addiing additional impedance into your supply cable which reduces its "performance", it will increase volt drop and earth fault loop impedance. (Physics)
If the joint fails, which it can you have a fire risk, and the possibility of the failed joint inducing a possibly lethal fault into the premises.
Without the full detail of how the actual install is to be/was done I can'f fully comment.
However, it is not good practice, which is actually against building & electrical regs, as there are better and safer ways of doing it.
There is a section in Part P & other building regs docs that requires "good materials & workmanship", which is basically mirrored in the wiring regs, I don't have the docs to hand at the mo, I am only still here as I am eradicating a virus from my daughters laptop which she desperately needs for her GCSE course work!!!
We can keep discussing this and I will try to find specific references if necessary.


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## Deejay (28 Feb 2011)

Morning Paul

I think you misread the post.

The use of an adaptable box on the outside removes the need to bend the SWA. The long tails don't add another joint if they terminate directly in the CU.

I'd still like to know if it contravenes the reg's.

Cheers

Dave


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## Dibs-h (28 Feb 2011)

NetBlindPaul":2rnrp9el said:


> IF you use a screwed joint, such as a "chocolate block" this has to be accessible for inspection. (Regs)
> You are addiing additional impedance into your supply cable which reduces its "performance", it will increase volt drop and earth fault loop impedance. (Physics)



I am sorry, but such rather fantastical claims, one hears a lot with absolutely zero calculations or real theory to back them. A block as has been suggested - how much extra impedance would it add? Do you know? What voltage drop would it add? The words practically NILL spring to mind, for a block of the correct rating. As has been suggested - whilst I might not necessarily do it that way - why wouldn't it be accessible for inspection?



NetBlindPaul":2rnrp9el said:


> If the joint fails, which it can you have a fire risk, and the possibility of the failed joint inducing a possibly lethal fault into the premises.



A joint made using the correctly rated connector - what fire risk? What possibly lethal fault? Assuming the wiring is to the correct spec\design.



NetBlindPaul":2rnrp9el said:


> Without the full detail of how the actual install is to be/was done I can'f fully comment.
> However, it is not good practice, which is actually against building & electrical regs, as there are better and safer ways of doing it.



Not good practice - how so. Got any sections\clauses\sub-clauses to quote?

I'm sorry, if my post comes across as having a dig at you Paul - it isn't. When claims of x. y & z are made I like to see the substantiation up front. The fact that the word Engineer is over used in the UK and has no protection unlike in other parts of Europe, but that's just my pet hate! (that's probably just my Monday morning grumpyness coming out)

Dibs


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## kingcod (28 Feb 2011)

Dave - thanks for links - already in my set of bookmarks 

Rob - I agree Red ceiling joists look better - and less fiddly to fit. I might try to reduce the total number (1 every 2 rafters?) to avoid overkill. Snow loading - I am on Tyneside so 0.6 - 0.8 Kn/m2 (I think). Gawd knows what that means for my design!

Mike - I am trying to stick to wood so I hope 200 x 500 x c.7000 for my ridge. The I-beam sounds a bit scary to get up there.

Electrics - would something like *this* suit to terminate the SWA up at soffit level? Thinking on this I intend to get wired up for an alarm so wonder if the electrics should be tamper proof on the outside ....
Whatever happens I will get a qualified sparks to do it!


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## Dibs-h (28 Feb 2011)

kingcod":37d1h68y said:


> Thinking on this I intend to get wired up for an alarm so wonder if the electrics should be tamper proof on the outside ....
> Whatever happens I will get a qualified sparks to do it!



Tamper proof - that will mean bringing the supply in underground and bringing it up thru the slab. Anything else is not tamperproof.

HIH

Dibs


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## NetBlindPaul (28 Feb 2011)

Dibs-h":tk1lx6zg said:


> NetBlindPaul":tk1lx6zg said:
> 
> 
> > IF you use a screwed joint, such as a "chocolate block" this has to be accessible for inspection. (Regs)
> ...



Dibs,
I am qualified to practice in countries where the term engineer is protected in law I can assure you as this is one of my pet hates also! I won't list my qualifications, but I did an apprenticeship and then carried on to get letters. I was made redundant from a design/applications engineering post when several of our large customers closed down in the Midlands and the global recession was just starting. From then I went back on the tools, now I am flying completely solo.
I undertake craft type work and I also undertake engineering design & H&S consultancy.

I can quote you reg numbers but unless you have a copy of 7671 & know your way around it, this would be a bit of an overkill.

I will once I get the chance to pull up some references as I promised.

The fire risk is often seen when screwed connections are not correctly made, often by DIYers.
The potentially lethal fault can come from several failure modes, to do a full FMEA I would need the full details of the install, the upstream cct protection and the characteristics of the supply at the origin.

Please also remember that when an electrician comes to work at your home, this becomes his pace of work he thus has to comply with all work place legislation.
If he is to fit this for the constructor he has to also comply with CDM & work at height legislation, thus the joint must be in a position where by it can be inspected without the necessity of working at height as it is possible that live working could be needed at that location.
Thus remove the joint and you remove the requirement for access for inspection & testing at height.

Paul


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## NetBlindPaul (28 Feb 2011)

kingcod":lp6cub76 said:


> Dave - thanks for links - already in my set of bookmarks
> 
> Rob - I agree Red ceiling joists look better - and less fiddly to fit. I might try to reduce the total number (1 every 2 rafters?) to avoid overkill. Snow loading - I am on Tyneside so 0.6 - 0.8 Kn/m2 (I think). Gawd knows what that means for my design!
> 
> ...



kingcod,
If you utilise that box then you must be careful as you can experience plastic deformation of the body of the box, allowing the cable glands to loosen, this can allow a corresponding increase in earth fault loop impedance and a reduction in the sealing properties, i.e. IP rating of the enclosure. There is more to this than meets the eye.
Sorry.


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## Deejay (28 Feb 2011)

Evening Paul

_The fire risk is often seen when screwed connections are not correctly *mad*, often by DIYers._

Shurely shome mistake  

Cheers

Dave


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## NetBlindPaul (28 Feb 2011)

What mishtakkee?.... :lol:


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## Dibs-h (28 Feb 2011)

NetBlindPaul":2u5pukxb said:


> The fire risk is often seen when screwed connections are not correctly made, often by DIYers.



I understand where you are coming from - but most folk who self-build workshop, are way beyond the realm of DIYers and almost in the realm of some Pro's. In some cases, the work of Pro's isn't upto the same level. Some admittedly not all.




NetBlindPaul":2u5pukxb said:


> The potentially lethal fault can come from several failure modes, to do a full FMEA I would need the full details of the install, the upstream cct protection and the characteristics of the supply at the origin.



My own preference would be to bring the supply inthru a conduit into the slab, ensuring min bend radii are not exceeded. But obviously there is more than one way to skin a cat. A full FMEA analysis would be way overkill in this type of sceanrio - i.e. bring the cable up outside into an enclosure. But we can agree to disagree.



NetBlindPaul":2u5pukxb said:


> Please also remember that when an electrician comes to work at your home, this becomes his pace of work he thus has to comply with all work place legislation.
> If he is to fit this for the constructor he has to also comply with CDM & work at height legislation, thus the joint must be in a position where by it can be inspected without the necessity of working at height as it is possible that live working could be needed at that location.
> Thus remove the joint and you remove the requirement for access for inspection & testing at height.
> 
> Paul



Yes I agree. Working at height regs are there for a reason and it is encumbent on the contractor to carry out an assessment. But even in this scenario - no contractor is going to specify full scaffolding. I certainly feel that live working in the scanario mentioned is highly unlikely.

Yes remove the joint & you remove a few requirements but as with all things construction it's a trade-off. In this case the OP doesn't want to bring the cable up thru the slab - I would, but he doesn't. Again a cable being brought up outside into an enclosure, might not be the best method, but I don't feel it's an invalid method and that i feel is getting missed here. There is best practice and there's worst practice (i.e. illegal) but some things do fall inbetween, i.e. acceptable.

On the subject of connectors - ever seen a torque spec for tightening torque that should be used on screw down connectors? I doubt they're supplied much these days or even exist, except for the true industrial connectors.

Dibs


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## NetBlindPaul (28 Feb 2011)

Dibs,
It would be my preference to bring the cable through a duct in the floor slab also, however, there is nothing wrong with bringing the cable up the exterior of the building and then as i said entering through the soffit area.
An FMEA should be done as a routine part of any design exercise. It is the extent of the FMEA that should be limited.
We will have to agree to disagree on jointing a cable in an exterior enclosure when it is unnecessary then, which it is.
There is no reason for full scaffold, especially if you are not jointing the cable in an external enclosure.
Just because the cable does not come up through the slab does not mean it has to be jointed in an exterior enclosure.
Yes I have seen many torque specs even today for screwed connectors of a professional grade.

Please as I have already said, you will need to answer to your insurer, the LABC & others perhaps should an issue arise.


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## Deejay (1 Mar 2011)

Morning KC

_Mike - I am trying to stick to wood so I hope 200 x 500 x c.7000 for my ridge._

Sounds a bit big. Are you sure?

200 x 50 sounds better to me.  

Cheers

Dave


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## Dibs-h (1 Mar 2011)

Deejay":3lss1hh9 said:


> Morning KC
> 
> _Mike - I am trying to stick to wood so I hope 200 x 500 x c.7000 for my ridge._
> 
> ...



Yeah does sound big. When I said "bigger the better" I meant the workshop, not the ridge. :wink:


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## chipchaser (2 Mar 2011)

Hello Kingcod,,

The preferred method for bringing a supply cable into a building is via a duct rising through the floor. The duct could be a clay or pvc pipe eg a drain pipe because that would be easy for you to source. Some electricity boards use a black pvc duct. From memory your cable should be 450mm below ground level with mechanical protection, cast concrete tiles are often used if it isn’t in a duct, and warning tape above. 

At the building you need a gentle bend which will rise through the floor. If you have a plastic DPM carefully cut a star shape at the point where the pipe comes through and seal the turned up plastic with tape wrapped around the pipe. Builder’s merchants will have the right tape. You may already have bought some to seal laps in the DPM if you have a large floor.

You need to site the intake carefully so the cable rises in a suitable spot, easily and safely accessible for maintenance because ideally your distribution board will sit on the wall directly above the intake at a safe and convenient height. Avoid obvious poor locations like behind the inward opening door to your shed because you don’t want to be giving your leccy the kiss of life after pushing him into the live board he has just connected for you and so on. There should be a safe open area around the board in the finished building.

IIRC bringing the cable into a wall cavity is not acceptable, it certainly isn’t sensible, just awkward. Likewise it is just plain sensible to avoid unnecessary joints especially below ground.

Tha cable feeding your shed should be fitted with the appropriate protective device (RCD or RCBO) at the source (your consumer unit or a sub DB added for the purpose). There should also be a double pole isolator at the source as it should never be necessary to work live on circuits within your property.

HTH
Graham


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## NetBlindPaul (5 Mar 2011)

Couple of follow up points.

A cable installed in accordance with BS7671 no longer has a defined depth at which to be buried, it is up to the competent person installing the cable to ensure it is buried at a depth sufficient to prevent damage occurring.

You can bring cables in through cavities and run them through cavities as long as you can comply with all of the raft of legislation and guidance that is required to do this.

Underground cable must incorporate earthed mechanical protection, however it is not statutory to have additional mechanical protection such as tiles, however this is a blinking good idea!
The warning tape is required

It is not necessary to have a residual current device at the origin of the sub main circuit depending on the installation conditions and circuit design details.
In fact there is guidance to say that you should not install such protection there for certain types of installation.

It is illegal to work as part of a business undertaking on live circuits except in the situation where it is not possible to work with the circuit isolated.

Live working must only be undertaken by persons competent to do so with the necessary precautions in place.

There are requirements in legislation for clear space around DB’s.


With a new build and design there need not be such compromises, as these will be merely financial. Financial compromises where safety is concerned are a very grey area.
Please remember, even though you may be DIY and may be not running a business you still must comply with the building regulations, and really you must comply with CDM regulations if you delve into the detail. The reason being is that the premise may well be sold on in the future.

The building regulations require absolute compliance and they can be applied such that any non compliant works must be re-done in compliance, this remember includes the requirement to insulate structures, include natural lighting etc. no matter what the intended purpose / “person” constructing. LABC have within their powers to have the construction “removed”!

OK as far as the wording, goes the “Building Regulations” Regulation 7 requires that any building work which is subject to the requirements imposed by Schedule 1 of said regulations should be carried out with proper materials in a workmanlike manner.
If you are running a business undertaking from the premises concerned, then on top of LABC, you will have wither LAEH or HSE FOD to answer to should it be found that the installation does not meet the requirements of “accepted” practice. Which in such a situation as this would be how the sub main supply circuit would have been designed & installed by a specialist in the field. i.e. an electrician/electrical engineer.
If you are a hobby user working at home then should something go wrong then you will have to fight your insurance company to get the payout if they “smell a rat”.
They will spend considerable sums of money to avoid the payout if it is commercially viable to do so.
IF you check the small print of your house insurance policy, you may well be unpleasantly surprised!

As I was asked to back up my comments earlier with regard to the electrical installation then IF you want a BS7671 Reg. No. as to why you should not fit an external joint box to go from SWA to T&E in your sub main, try 132.7, 133.3, 134.1, 510.1, 510.2, 512.2, 513.1, 521.1, 522 (group), 526.1, 543 (some of this group),.
You would also need to refer to reg 422.3 when undertaking your internal install.

As I say business premises, EAWR89, PUWER98, MHSWR, building regs & your insurer, hobby premises building regs & your insurer will call the shots even if you don’t realise it.


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## Dibs-h (6 Mar 2011)

NetBlindPaul":1ht5ibph said:


> The building regulations require absolute compliance and they can be applied such that any non compliant works must be re-done in compliance, this remember includes the requirement to insulate structures, include natural lighting etc. no matter what the intended purpose / “person” constructing. LABC have within their powers to have the construction “removed”!



That's the theory - the practice is something else. That isn't a feeling - that's been borne out from experience. Most folk with the above impression\belief are rather shocked when the reality surfaces.


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## NetBlindPaul (6 Mar 2011)

Dibs, I have seen the reality also, however that is the statute law, one should not advocate breaking the law should one!


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## kingcod (20 Mar 2011)

So I have my concrete base in place now (pics to follow) and need to order up my concrete blocks. I am getting conflicting advice.

My design has a couple of rows of 440x215x100 standard blocks topped with a timber frame and timber roof. I am hoping to use the lightest blocks possible as I have to barrow them such a distance to the site. A builders yard is saying I need 7n dense blocks but surely I can get away with aerated blocks of the 3.6n variety? the blocks are above ground and are load bearing.

- oh and would hollow blocks do? I am thinking of using these to inset anchor bolts in for the sole plates. A bit like yer man here is doing:


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## Dibs-h (21 Mar 2011)

NetBlindPaul":2iqt66gc said:


> Dibs, I have seen the reality also, however that is the statute law, one should not advocate breaking the law should one!



Not in the slightest - I was referring to the rubbish that local BR departments of Councils will and do pass. Not the slight's of hand the builders\clients will pull.



kingcod":2iqt66gc said:


> So I have my concrete base in place now (pics to follow) and need to order up my concrete blocks. I am getting conflicting advice.
> 
> My design has a couple of rows of 440x215x100 standard blocks topped with a timber frame and timber roof. I am hoping to use the lightest blocks possible as I have to barrow them such a distance to the site. A builders yard is saying I need 7n dense blocks but surely I can get away with aerated blocks of the 3.6n variety? the blocks are above ground and are load bearing.
> 
> - oh and would hollow blocks do? I am thinking of using these to inset anchor bolts in for the sole plates. A bit like yer man here is doing:



You would need to talk to a structural engineer as to what the compressive strength needs to be for your plinth. No different in my mind to the plinths that are used in masonry construction, i.e. the 1st few rows on a brick house will have engineering bricks and then normal bricks.

I personally don't think 3.6N blocks would be sufficient, as it's not just the static load they have to bear up to, but also the dynamic loads due to wind, snow, etc that are transmitted thru to the foundations.

In the absence of paying for an engineer - I'd play safe and use the 7N blocks.

As for lugging blocks - I had mine delivered round the front, moved them 1 at a time, down a 3 car length drive, past a single garage, down 5 steps and finally 3m's down the garden and onto the site. And that was 9 full packs. So I think you've got it easy, with less blocks and a barrow! :lol: 

HIH

Dibs


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## kingcod (24 Mar 2011)

The 7N blocks are all set to go. An hours work with a barrow to get on site . I am now puzzling over the position of the DPC and the sole plate. If I am resting the sole plate directly over the DPC can I still fix anchor bolts / paslode shots through the DPC into the concrete blocks? Surely thats another compromise on the DPC layer? I can't seem to find a simple alternative. I am looking at straps to fix the sole plate but not sure where to fix them at the base. If only I had followed the full Mike Garnham technique and concreted straps into the base. *sigh*

Would a DPC between the first and second course of concrete blocks do any good? Or would that make mortaring up the blocks a bit difficult?


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## Dibs-h (30 Mar 2011)

kingcod":2iv15v8r said:


> The 7N blocks are all set to go. An hours work with a barrow to get on site . I am now puzzling over the position of the DPC and the sole plate. If I am resting the sole plate directly over the DPC can I still fix anchor bolts / paslode shots through the DPC into the concrete blocks? Surely thats another compromise on the DPC layer? I can't seem to find a simple alternative. I am looking at straps to fix the sole plate but not sure where to fix them at the base. If only I had followed the full Mike Garnham technique and concreted straps into the base. *sigh*
> 
> Would a DPC between the first and second course of concrete blocks do any good? Or would that make mortaring up the blocks a bit difficult?



I don't see why you couldn't set anchor studs into the blockwork and then lay the DPC on top, with holes for the studs to poke thru, then use washers and nuts to hold the soleplate down. You could always seal around the studs with a construction sealant if you have any concerns regarding compromise.

I would put the DPC under the soleplate.

HIH

Dibs


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## johnf (31 Mar 2011)

The dpc should be on below the first course of concrete blocks directly on the slab which should be 150mm above the external ground level 
You can then build fixing bolts into the vertical joints or just plug and screw the sole plate directly to the blockwork 
ps 4/1 mix for the mortar


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## kingcod (5 Apr 2011)

So a bit more progress to report on.




Site ready for concrete: shuttering, DPM, steel mesh supported to 'float' inside the concrete pad.




A gut busting day of barrowing lots of concrete



It takes 5 of us about 2 and a half hours. The guys from the concrete truck can't quite believe the 100 metre hill between the road and the site. Extra beers for their efforts.




The wonderful numpty proof 'Bricky' makes the blockwork easy




Blockwork all done with a DPC sitting between the two tiers of blockwork.

I have a few questions but will post them when I have my thoughts together. 

oh- the sole plate I reckon will just be fastened directly into the blockwork with masonry fixings.


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## johnf (6 Apr 2011)

So what stops the damp rising into the bottom course of blockwork 
PS I am a bricklayer of 45 years experiance


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## Dibs-h (6 Apr 2011)

johnf":2sehpmfc said:


> So what stops the damp rising into the bottom course of blockwork
> PS I am a bricklayer of 45 years experiance



If there hadn't been a DPM under the concrete I would have thought nothing, but looking at the earlier pictures - there's a DPM under the concrete, in which case a DPC appears pointless.

Dibs


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## kingcod (6 Apr 2011)

Dibs-h":1h0odbv3 said:


> johnf":1h0odbv3 said:
> 
> 
> > So what stops the damp rising into the bottom course of blockwork
> ...



Yes there is a1200 guage DPM under the concrete. As for the DPC ... I was just following Mike Garnham's design which shows both:

build-a-shed-mike-s-way-t39389.html


Which brings me to a few questions:

1. Double sole plate or single sole plate? I have seen designs with both.
2. How to treat the DPC at the doorway. If you can imagine it appears out the wall at i block height ... should I extend it down and around the base of the door frame and door step (which will all be in wood)?
3. Any special treatment needed for the wood fram, particularly the sole plate as the most potentially exposed section? Do I need tanalised timber or will Kiln Dried C16 do?
4. screws with an impact driver or ringnails with an air nailer to stick build the frame?
5. Should I fastidiously protect the half built frame from the weather or just work on and let it dry through once it gets clad?

Thats it. Advice greatly appreciated


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## Dibs-h (7 Apr 2011)

kingcod":3q2p54nv said:


> Dibs-h":3q2p54nv said:
> 
> 
> > johnf":3q2p54nv said:
> ...



1. A single wall plate should do. I don't see the advantage in a double one.
2. yes extend it down and under the door frame\step.
3. I've used normal timber, but mine was behind a block wall. If exposed, might be safer to go with a treated one. You cpuld always use DPC under it and then wrap it round over the top, from the outside of you wanted. I'd be inclined to use normal timber. Then frame wrap it and make the counter battens go below the sole plate and fix the ends into the 1st course of blocks. That way your cladding (fixed to the counter battens) extends below the sole plate and you shouldn't have any issues with moisture.
4. Screws and impact driver are definitely the way to go, especially of you need to make adjustments. DAMHIK!
5. Protect it as best you can, but no need to go OTT. Dry it out once wrapped in building\frame wrap.

HIH

Dibs


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## defsdoor (12 Apr 2011)

kingcod":1cbst1qu said:


> As for the DPC ... I was just following Mike Garnham's design which shows both:
> 
> build-a-shed-mike-s-way-t39389.html



The DPC on that diagram is between the blockwork and the sole plate - which is part of the timber construction. On yours isn't it between two courses of blockwork ?


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## kingcod (12 Apr 2011)

defsdoor":3a3d6vyy said:


> kingcod":3a3d6vyy said:
> 
> 
> > As for the DPC ... I was just following Mike Garnham's design which shows both:
> ...



Yes correct. I have tweaked the design. I did this because I hadn't done enough planning to use straps set into the concrete to hold down the sole plate (and also thought it looks a bit flakey as a way of holding something down). I wanted fasterners fixed directly through the sole plate into the blockwork .. but clearly I can't do this with a DPC in between as it would puncture the DPC. Hence the DPC set one course down. Its still got above the 150 mm ground clearance you need for a DPC.

I hope this is all going to work out as the timber arrived so the sole plate goes in tomorrow!


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## defsdoor (13 Apr 2011)

Is that ok like that ? (I know nothing but read all the workshop build threads as I have a small brick shed at the bottom of the garden that I would like to make bigger at some point)

With the dpc underneath the sole plate, which is firmly fixed into the course below, I'd feel more confident that things couldn't move.


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## johnf (13 Apr 2011)

Well for whats its worth in my opinion the DPC should be directly on the concrete slab witch should be 150mm above the surounding ground level in this situation there is no need to put a DPC below the sole plate just bed the plate on with mortar and fix with masonry fixings or screws when the mortar has gone hard.
In 45 years trading as a building contractor I have done loads of buildings like this and no problem with any of them.


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## kingcod (14 Apr 2011)

John - since the ground is on a slope (you can't really see on the pics) the slab is down to ground level at one end and way up around 150mm above ground level at the other end - otherwise I could have done as you suggest. 

I'm still mulling over what to do with the DPM where it appears out the end of the slab ... I am not sure cutting it off at this point would be a good idea as I assume I'd get damp ingress into the concrete slab. Should it be up round the sides fo the block in some way?


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## johnf (15 Apr 2011)

kingcod":ohq5qvyf said:


> John - since the ground is on a slope (you can't really see on the pics) the slab is down to ground level at one end and way up around 150mm above ground level at the other end - otherwise I could have done as you suggest.
> 
> I'm still mulling over what to do with the DPM where it appears out the end of the slab ... I am not sure cutting it off at this point would be a good idea as I assume I'd get damp ingress into the concrete slab. Should it be up round the sides fo the block in some way?



Kingcod If you mean the dpm below the slab you can do as you sugest but if its exposed to weather and sunlight it will eventualy fail


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## kingcod (16 May 2011)

I'm having a think about cladding insulation and all things to keep warm, toasty and dry in the workshop.

I quite like the look of larch featheredge cladding as a cheaper alternative to oak. 

The advice I have read so far for featheredge seems to suggest the need for Tyvek or similar underneath the Tyvek to keep out wind and expel moisture. Then there is the additional suggestion of a vapour barrier on the inside of the building just below the plasterboard. Looking at my diagram of all this below is two vapour barriers overkill or are they doing slightly different jobs? If so whats the cheapest material I can use for the vapour barrier or is there a hard to avoid industry standard 

For simplcity the diagram doesn't show the timber frame.


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## JanneKi (18 May 2011)

That's the right way to do it actually, but you have to ensure there is enough ventilation space between the Tyvek and the actual cladding. Why use larch, that's expensive stuff (at least here in Finland)? Tyvek and the vapor barrier actually do different things:
- vapor barrier keeps moisture out of the insulation, by not letting (the presumably warmer and moister) air enter the insulation.
- Tyvek lets moisture (in gas, i.e. moisture in the air) OUT, but does not let water (in it's liquid/solid shape) enter into the insulation.

In Finland (and Sweden) we user normal spruce/birch for the cladding, but we paint it then (usually). That works pretty well, even with Latex paint - AS LONG as you have sufficient ventilation gap BEHIND the cladding, typically minimum of 20-20 mm - of non-restricted air flow. In certain sense that is a fire hazard, but it required to keep the cladding healthy - paint cracks eventually and the moisture that gets into the wood can ventilate/dry out from the non-painted backside of the wood.


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