Shed / Workshop Build

[MikeG.]

So why does the stud wall want a vapour barrier but not the blockwork?

If there needs to be a DPC between the blockwork and the timber then that must imply that the blockwork might get damp right? Is that not going to be a problem inside since it's a single skin wall?

Remember that this isn't a house. The moisture in the inside of a shed is not comparable with a house.....think kitchen, baths, showers, washing machines etc. The danger with moisture and a timber frame is that condensation will occur within the structure.........hence the need to keep things dry by isolating the frame from the moisture source. This isn't an issue with masonry.

There isn't a huge need for the DPC under the frame............it must be included, but it is a bit belt & braces. The taller the plinth, the less the DPC is doing. Don't forget that bricks work by absorbing moisture and then releasing it slowly (which is one reason not to use the sealants sold for waterproofing brickwork).

Mike

 

[chipchaser]

Excellent shed Dave. Good deal on the window and nice to see it being put to good use rather than going into landfill. If anyone in the Coventry area is looking for a shed window there is a firm who have recovered or misfit uPVC windows for sale. They are on the road from Toolstation towards the M6. Have not checked any prices or details but maybe worth looking?

Mike is right about the ties needed to resist outward thrust of the rafters. If it is now difficult to install ties with spreaders and nuts on the outside, several of your wire ties with fixing points coach screwed to the inside of the wall plate can work as well as a couple of more substantial ties. Obviously eye bolts through the plate with a good square washer and nut on the outside would be better if that is possible.

Have you tried opening your “lost” pictures with Irfanview? I had a trojan attack my hard drive last year but luckily recovered a lot of my files using Recuva. Irfanview opens many, but not all, of the photos which Windows Picture Viewer won’t open. I can then re-save them as .jpg in the same folder after which Windows will open them.

Regards

Graham

 

[dh7892]

Dave and Mike,

Thanks again for the replies. So the aim is to deal with letting water vapour leave the shed, not because of any worry about watter getting into the shed.

So there's no problem with a single skin of blockwork wicking enough water through from the elements to, say, damage the paintwork on the inside?

 

[Haldane]

Hi dh7892

Sorry can't help anymore I'm no expert and nearly all the info I needed for the shed build came from members of the forum. Hope someone (mike) may be along shortly and help out with an definitive answer

Dave

 

[chipchaser]

Hi dh,
Mike has answered the question in general terms. To get a better understanding of your situation and to comment usefully needs a bit more info:

1) What sort of blocks (dense concrete or lightweight like Celcon or Thermalite or another type) and how thick?
2) Internal and external finishes, if any?
3) I think you said single skin of block with no insulation or external lining at present, do you intend to add an internal lining or external cladding?
4) Workshop or storage?
5) Anything in the shed that produces water vapour e.g. an unvented washing dryer?

Regards
Graham

 

[dh7892]

I'm only at the very early planning stage but, since this build as almost exactly the size I have earmarked for mine and would suit me fine in almost every respect, I was going to pretty much copy it.

I would only be having wood working stuff in it (no tumble drier). I have no idea of what sort of blocks I would use. I was just going to go with something similar to Dave's build.

My only question though was about the fact that the blockwork had no cladding on it and I wondered if water would wick in and cause problems. I'm sure it is fine or Mike would have said something.

Anyway, I don't want to hijack the thread. It's a great build! I hope I can end up with somethign similar.

 

[MikeG.]

DH,

Use bricks instead. Aesthetically more pleasing, and perfectly simple to lay. You only need 2 courses. One of the keys to success is to have the slab about 50mm above ground level min., all round, and then have you render or cladding overhang the junction. This will actually mean that very little water will ever make any contact with the masonry plinth, be it brick or block.

Don't forget, your timber frame comes flush with the outside of the bricks/ blocks, then breather membrane, battens and boarding, meaning your finish overhangs. The bottom edge of your boarding or render is some 50mm outside the line of the brickwork, so all the water that runs down the walls has a good chance of dripping clear of the brickwork.

Very little moisture will rise up the edge of your concrete as it is on a membrane, and any that does has a chance of drying off because the top edge of the concrete is well above ground. So the half-brick thick wall is relatively dry from both above and below, and will dry off quickly.

I can tell it works, because in those corners of the workshop where sawdust gathers next to the bricks the sawdust always sweeps up dusty like all the rest, rather than being at all wet.

I can't stress enough......(but goodness knows I have to!!!).......what a huge difference a plinth makes. It is the difference between a temporary shed, deteriorating as soon as it is built, or workshop, there for decades.

Mike

 

[dh7892]

As in the common or garden red house bricks? Sounds like a plan.

Thanks for the advice.

I like the idea of the 10mm studs cemented in the brickwork to attach the studwork to. If I'm using brick, would I get enough purchase with one brick's worth of mortar for the studs to sit in?

Is there a recommended depth for the foundations (roadstone and concrete) for such a big area. Also, would re-bar in the concrete be a good idea?

Cheers,

Dave

 

[MikeG.]

Lots of questions there DH!

I wouldn't use the studs method myself. I prefer to cast galv. steel straps into the concrete and fold them over the wall plate. Alternatively you could build them in under the brickwork (L shaped straps), but I would want to see at least 3 courses of bricks in that case.

As for foundations.......build it so that you dont require Buiding regs (ie small enough and away from boundaries), and you can omit foundations and just build off a slab (say 6 inch conc. Yes, in that circumstance I would put mesh in it. Don't do this if there are major tree roots through the site.......and thicken it up if you are on clay. Treat this part of the advice with caution.......investigate your site circumstances before designing a slab/ foundation.

Mike

 

[dh7892]

Thanks,

I think I'm going to need both permission and regs as I need to be up close to a fence and I want more than 15 sq m.

 

[Woody Alan]

Mike,

I have built a couple of buildings that I took straight off a slab.
here's one

I have since moved and will be doing something similar. I have a question about your preferred method of a couple of courses of brick. How do you make good and insulate tidily on the inside of the building or do you accept a cold bridge? and do you have to frame in 4" so as to span the brick? but that still gives a cold bridge at the base.

Cheers Alan I need to get the next one right

 

[MikeG.]

Alan,

yes, I just accept the cold bridge. Given the occasional heating and low moisture-production in a typical workshop it cause no problems at all. Having said that, there are a number of ways in which you could insulate the inside of the plinth if you really wanted to, such as by overhanging the frame an inch inside the brickwork, placing an inch of Kingspan inside the bricks, then bringing the inner skin of sheathing board down to the slab.

You don't have to frame in 4", but for that size of building I would be uncomfortable seeing it built of 3x2s, and don't really see what you would gain. You could use 5x2s, and thereby create the overhang I spoke of allowing insulation of the plinth, but it seems to me that might be an expensive sledgehammer to crack a very unimportant nut.

It is a pity you put such a lot of effort into this workhop and still ended up with something you aren't completely happy with.

Mike

 

[jack55]

Nice workshop build I like a few others it seems are planning a similar build in the summer. The roof design gives lots of head room and I would like to do the same. Would that design work on a 14 foot wide by 18 foot long shed? and are the metal rope ties the only way of stopping the walls spreading.

Link to big picture

 

[MikeG.]

Jack,

it would be nice if you could re-size that drawing to make it 800 wide so that we don't have to scroll sideways to see it all.

There are lots of ways of doing rooves. You appear to be showing a post at the gable to support the ridge......and if you have a substantial structural ridge beam, calculated to support all of the roof-loads , then you won't need any ties to prevent the roof spreading. However, this relies on an 18 foot long piece of something......probably a glulam beam or composite "I" beam, even a flitch beam (steel & timber).....that doesn't deflect under the imposed load.

You could do old-fashioned Principal trusses with intermediate common rafters supported on purlins and even a ridge purlin.........meaning that you wouldn't need any ties. You would probably be best with just one central principal truss.

The simpler and cheaper way is to tie across at roof-plate level. This doesn't need to be at each rafter, and with a substantial and continuous roof-plate you might be able to only use a couple of ties in 18 feet. This tie could be tensioned wire, but it is probably better in steel rod or timber.

The other thing to consider is having ties at every rafter, but have them raised (collars/ raised ties). Typically they work best around one third of the way up the rafters. You could combine raised ties with purlins, so that you didn't have to have ties at each rafter.

I would stress that none of this is to be done by guesswork. Whatever you propose should be checked by someone competent. I'm not a structural engineer, so if you require building regs for this then I am not qualified to prove the structure. However, if it doesn't require BR approval, then I can design the roof for you without any problems.

I hope this helps.

Mike

 

[jack55]

Thanks for the offer Mike. I will put in the form to see if I need BR, going to keep it within the 2.5 eaves height and overall less than 4 with 1.5m from the boundary wall and see what they say. SWMBO's greenhouse roof suffered from the weight of the snow which bent the roof ridge beam and the support bars. Although a lot lighter it is a similar design. Forgot about the drawing width my comp screen is 22" so it all shows on this.