Workshop Design - well it's a build really.

[Dibs-h]

Question\Advice: Originally there was to be a screed floor (over a DPM which will be lapped to the DPC that pokes out inside) with a single row of blocks butted upto the outer leaf of blockwork, inbetween the piers. A 4"x2" baseplate was to be screwed to this and then the inner stud wall built upwards. As these blocks would have been laid first and then the concrete screed - the blocks wouldn't have gone anywhere and the tendency for ethe stud wall would have been resisted by the screed (very well).

Now - there's not going to be any screed. So Plan B is to lay the DPM and lao it to the DPC (as original plan), lay 4"x4" pressure treated (or normal) timber where the blocks would have gone down - between the piers and up against the outer blockwork. Lay 50mm kingspan down on teh DPM and then 3"x2" bearers on top, screwed to the 4"x4" locking everything together. Then building the stud work off the 4"x4" baseplates in essence. Now since the 4"x4" are sat on the DPM which is continious - I feel there won't be any issue with there being no ventilation, etc.

Good idea or bad idea?

I can't really use the blocks as the even with mortar there is no screed tying them togther anymore. May well have to make a decision fairly soon.

Also - in a few places could do with leveling the slab - was thinking of a sand & cemet mix (just so there are no voids below the insulation), sharp sand with cement or building sand with cement? Or not matter? (I have some building sand left over). In either case - what sort of mix\ratio?

Thanks.

 

[big soft moose]

looking good - what are the dimensions ? as it looks huge - not unlike my house in fact.

Just over 4m wide and 7.5m long, and around 4m at the ridge.

nice space - thats about half my house - bet you're looking forward to the set up/fit out phase , thats always my favourite bit

 

[crazylilting]

I'm trying to understand the predicament your in Dibs-h. Is screed just a top coat on an already existing cement slab?

From the pictures of the floor it looks like there is nothing there.

What I would do which will probably be shot down by others would be to level off the dirt floor inside and put a layer of sand and compact it.


Put your damp proof membrane down leaving it wild up the wall past where your finished floor will be

Run 1 - 4 x 4 down the center of the building providing you have something for load bearing. I would also bolt some squish blocks to the outside wall to the same level as the top of the 4 x 4.

Paint the blocks with a damp proof tar product not sure what it's called in the UK. Several coats and then seal the membrane to the damp course so that the one poking through the blocks is pointing up like an L. Laminated to the wall with the same tar.

Then i would bolt a ledger plate to the entire outside walls leveling the bottom with the top of the 4 x 4. I would use 6 x 2 for the floor on 16 inch centers and cut the kingspan to fill the floor joist spaces even with the top of the joists and sheet the floor with as thick plywood as you can afford.

Then wrap the membrane under the bottom plate of your 3 x 2 stud work so you can attach your vapour barrier to it and have a complete seal. For ventilation i'd drill two holes in the stud work through the floor at each end of the building and hook up an inline bathroom fan to one of them drawing fresh air in and the other exhausting it out of the building.


To further protect i would tar all block work bellow grade outside, lay a perforated pipe and cover with clean pea gravel, I don't know if you have a sloping grade but if you do you can send the pipe in that direction. Then cover that with a good quality landscaping fabric and back fill to grade.

It doesn't look like you have room for vented blocks so that would be my way around it.

 

[Dibs-h]

Yes in my case screed would be a top coat on an existing structural slab.

Nothing there - man I nearly died leveling that slab - 6M3 of C35, I'll have you know. Only kidding - you probably can't see it because all the leaves off the trees are in the workshop, composting on the floor.

You're not a million miles off. I already have a slab - 8" thick IIRC (well a raft - but what's in a name). It's just that water pools in a few places - so was thinking of sand\cement mix to level off.

On top of this slab\raft, beacuse it isn't insulated - was to be the DPM, 50mm insulation and a 50mm anhydrite (or thereabouts) screed. The 1 course of blocks inside that would have served as the base of the stud wall would have sat on the DPM, and the screed would have bonded nicely. Now because of the cost of pumping, and drying times - can't be arsed with it. So onto Plan B.

If I place 4"x4" on the DPM, the stud walls sit on it (it effectively becomes the baseplate) - normally the baseplate is screwed\bolted down. But I don't want to pierce the DPM - so was thinking that if, in the floor the 3"x2"'s go from the back wall to the front wall - everything should lock nicely together.

Also I would have screwed some of the studs to the block wall - but they are 4" deep - so that would have to be some big screws!

In essence I suppose what I'm thinking of is not screwing the baseplate on a stud wall down to the slab, but relying on the floor joists to stop any tendency for the bottom of the studs to kick inwards (as they would be tied together). I'm probably over-egging the pudding - the studs from a strutural perspective transfer the load down from the pole plate to the slab - there isn't enough moment to cause the bottom of the studs to "kick" inwards.

 

[chris_d]

Also I would have screwed some of the studs to the block wall - but they are 4" deep - so that would have to be some big screws!

You could counter bore the studs to 2" with a bit that is the same diameter as the screw head, then use cheap 4" screws and plugs to attach them to the blockwork. From what I can see, the stud walls are only supporting the boarding on the ceiling and walls, so don't worry about compromising the structural integrity of the stud with the counter bore.

Simples.

 

[Alex]

Dibs, are you going for suspended wood floor? Much better IMO
A 2" screed over insulation is not thick enough even with reinforcement for any floor carrying machinery. A screed for this floor i would also split into four with expansion gaps. And then there is the final floor finish to concrete to think about. Wood floor is sooo much easier.
Crazy's part right i'll just adjust it slight bit.
Right suspended wood floor needs ventilation.You need to work out best way of achieving this. Run supporting base joists level round the perimeter 4"x2" bolted/plug and coach bolt every 2' to the wall. I'd staple some dpc to the face of the joists that touch the wall. Now put in your 3x2" joist at 400mm centres remember to put support under or feet screwed to the side of the joist every 4'. This is so no joist is more than 4' unsupported. These 3x2" joists are suspended of the perimeter joist with joist hangers or can be notched into. Now put nogging between joists so they carn't twist should be every 6'. Now put extra supports in for the stud wall if it runs adjacent to joist it means extra feet it it runs with floor joist i'd double up or even triple the floor joist under wall so you have something to screw floor to.
Cut your 2" PU insulation tight fit between joists. Mark on walls where the stud wall goes and screw your p5 chipboard down then build stud wall on top. Remember stud walls are temp after all.
It would take me by my self 2 days, no mess, no fuss and your hand tools will love it.

 

[crazylilting]

You're not a million miles off. I already have a slab - 8" thick IIRC (well a raft - but what's in a name). It's just that water pools in a few places - so was thinking of sand\cement mix to level off.

If you have 8 inches of concrete there why would you be worried about screwing into it? Wouldn't the damp proof membrane be under it? screwing in a 8 inch bolt through a four inch piece of wood leaves four inches before you even reach the membrane. Doesn't it?

Why did you need an eight inch slab? is this also part of the footings? K i went back and looked at the whole project again. I understand now that the slab is not just a slab it is also a part of the structural integrity of the stone wall behind the shop. However I didn't see any damp proof membrane go under this slab. In fact it is tied to the footings via rebar and steel mesh.

So at this point the only damp proofing is between the blocks that i can see or have seen looking through the pictures provided, unless there was two pours and a membrane was put in that I didn't see.

In that case i would use marmox boards and adhere them to the slab, they will provide a bit of insulation and a water proof membrane. I would also take them up the wall to the damp course you have installed and adhere that to the boards. Then you can either screed or put down your 3 x 2 s and insulate in between those. Essentially you'd be tanking the floor and the bottom portion of the wall up to the damp proofing.

 

[Dibs-h]

Essentially you'd be tanking the floor and the bottom portion of the wall up to the damp proofing.

Yes - the "tanking" is on the inside - so I don't want to pierce it.

Whilst an ordinary 50mm screed isn't strong enough - but from the specs of them anyhridte screeds are more than capable at 50mm. They do however require a final finish layer.

I think the idea of "counter boring" sounds good.

If we work on the assumption that the dpm\dpc form a "tank" then ventilation shouldn't be an issue, and can't really be introduced either.

 

[Dibs-h]

Update: Just spent all day cutting the infill blocks, for the rafter feet to poke thru. 40 cuts in about 30 odd blocks - thankfully the Stihl fired up and with a new blade made relatively light work of them. Only down side - the fitting doesn't seal properly for the water kit - so got p1ss wet thru in the bargain - but thankfully all done.

Thought it best to get them all cut and checked before mortaring them in tomorrow along with screwing the rafters down. I'm hoping to get the gables cut tomorrow and the straps fitted. I think the aim will be to get it Tyvek'd and counter battened (picked up 3 packs of 2"x1" laths on Sat).

It's gonna be a tight this week - but going for bust (preferably not A&E type of bust).

Will post up some piccies tomorrow.

 

[Triggaaar]

man I nearly died leveling that slab - 6M3 of C35, I'll have you know.

Pathetic I tried to level 27m slab of c35. But then I didn't do a great job and there was 2 of us.

Anyway, to the topic - my slab is like yours, and my plan is to hammer and boster any nasty sharp bits out, put some blinding sand down (left over building sand), then DPM, Kingspan, Vapour barrier, 22mm chipboard. I don't know if that's a good plan or not, but it is at least a plan.

 

[Dibs-h]

man I nearly died leveling that slab - 6M3 of C35, I'll have you know.

Pathetic I tried to level 27m slab of c35. But then I didn't do a great job and there was 2 of us.

6m3 - that was the entire floor area = 4.1m x 7.5m = ??? :wink:

Anyway, to the topic - my slab is like yours, and my plan is to hammer and boster any nasty sharp bits out, put some blinding sand down (left over building sand), then DPM, Kingspan, Vapour barrier, 22mm chipboard. I don't know if that's a good plan or not, but it is at least a plan.

I wouldn't have thought you'd need the vapour barrier - seems unnecessary as the DPM shold be doing it's job. I was thinking of sand (and cement mix) but will be going with some self levelling.

 

[Triggaaar]

6m3 - that was the entire floor area = 4.1m x 7.5m = ??? :wink:

Yeah I know. You did well to get away with 8" all the way. I was trying to level 27m3 over a slightly bigger area, but like I said, I've had some help.

I wouldn't have thought you'd need the vapour barrier - seems unnecessary as the DPM shold be doing it's job. I was thinking of sand (and cement mix) but will be going with some self levelling.

Indeed the vapour barrier does seem weird. It's not to help the DPM, but to stop vapour going from the room into the insulation, whether it's really necessary or not I don't know. If going self-levelling I'd recommend the Wickes deep compound, which is buy 3 get 1 free = £8.80 a bag (although as I posted in a previous thread, most of these levelling compounds are supposed to be above DPM, but I don't suppose that will matter for your use).

 

[Dibs-h]

Bloody annoying - just about to go outside and it's chucking it down. 5 mins in that rain and a drowned rat would spring to mind!

 

[Mattty]

Horrible morning in Leeds to mate.. I had to open the windows in my workshop as the stove was to hot 8) :lol: 8)

 

[Mr Ed]

You're just playing at laying concrete slabs here lads - this is the slab I did today (well I say 'did' I mainly point and wave my arms and other people do it...) just over 200M3;

Telescopic 360 degree laser screeding machine - thats the way to level a slab...might not have fitted in your garden though Dibs :lol:

Ed

 

[Mattty]

That would make a nice workshop Ed!

That is a serious piece of concreting, i don't think i'd like the responsibility of laying that one.

 

[Triggaaar]

Telescopic 360 degree laser screeding machine - thats the way to level a slab...might not have fitted in your garden though Dibs :lol:

That's more like it. Could have got it in my garden, assuming it's no more than two and a half feet wide.

 

[Dibs-h]

Probably cost more than my workshop build budget!!

Came back in this evening around 17:30 - looking and feeling like the proverbial drowned rat. Cold to the bone!

All I managed to do was "notch" for 4 rafters (in the corner blocks that were mortar'd in previously) and mortar'd all the others in. Left them with plastic covering them - hopefully stop the rain affecting the mortar.

Tomorrow looks ok weather wise so hopefully get the gables cut and then on with the rafters and Tyvek. Be well chuffed if I can get the Tyvek on.

Just need to work out the size, etc. of the tilting fillets on the end of the rafters - as the fascia won't be supporting the last row of (eaves) tiles. Probably lay a few tiles and work it out in situ.

If I'm lucky will get the inside swept and washed out ready for levelling of the slab.

 

[Dibs-h]

Update: Well it's certainly been a busy week, the expression "a drowned rat" would probably be a good description of how I ended up most evenings.

1st plan of attack was to cut the notches in the last row of blocks, for the rafter feet to poke thru. Spaced the rafters out and marked the blocks, then with the Stihl, cut several slots and then chiselled out the waste. Mortared them in place.

Then cut the gables. Didn't use the water attachment as it leaks and when I was cutting the rafter notches in the final row of blocks - I got soaked.

Screwed the rear rafters into the pole plate and the purlin - didn't screw them into the ridge (thought it best to do both sides together at the end).

Also cut off the overhanging purlins, pole plates and ridge on the side that the new garage will abut to.

That took most of the week strangely enough - far longer than I thought.

Then on Friday, got the front rafters screwed in (and both sets screwed to the ridge) - had to nip out and get more screws - 200 just don't seem to go far!

Finally managed to get a length of Tyvek on both sides at the top - overlapping it over the ridge.

That was at the end of Friday.

Then worked out the tile overhang, lath spacing and fillet size and got the second lot of Tyvek on.

The overlap on the Tyvek was marked as 6" - but as I was taping the joints I reduced it to about half, which gave me enough overhang at the eaves. It was amazing to suddenly no longer be getting wet when it rained!

Here's a shot from inside - the roof does look fantastic!

The lengths of 4"x2" being stored in the roof are for the internal stud wall, but as I had several trees worth of leaves on the floor - placed them up in the roof, whilst I cleaned up and washed the slab. Here's the slab having been cleaned of all the crap, but being hosed down.

In the end went and got the Karscher and blasted it all clean and then got rid of most of the water, with one of those rubber bladed thingy's on the end of a mopstick. Finally mopped up - hoping that the less water is on the slab - the quicker it should dry out, what with the door and windows not being there.

There's a lot more of the slab that will need SLC - so assuming I can get some temporary lighting sorted inside - that's on the list for this week and then the DPM and stud wall. I need the stud wall up before the tiling as the stud wall supports the pole plate.

Nothing happening for Mon\Tues as I have other stuff to do - hopefully crack on Wed evening with the SLC.

 

[houtslager]

looking damn goodfrom inside AND outside.

lucky bugger , wish I was so far in my build too

hs