Large poultry/workshop building

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8 Jun 2020
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Hello all, I’m after some specific advice in relation to a purely timber outbuilding I’m going to be constructing fingers crossed before this summer is up. It’ll largely act as a breeding unit for my poultry but it’ll also harbour some space for tinkering. Apologies if I switch between metric and imperial aswell.

I come from an unusual working background, I’ve worked a number of years in the zoo industry aswell as within construction industry primarily as a plumbing and heating engineer but I’ve built things with timber for as long as I can remember. So I own most power tools and I’m also quite competent at most aspects of studwork but it’s the nitty gritty methodology that I’m wanting to get my head around.

It’s going to be 7.32m long by 3.6m deep, the initial joists are reclaimed 7x3” joists and the remaining will be treated 6x2”. One side will be suspended off the ground to allow for undulations under food, going to postcrete some 10x5” sleepers into the ground to support the side that is elevated. The other side will have various posts knocked in the pick the shed base strength and take any bounce out of the framework.

I’m not so much worried about insulation because it’ll be an animal building ventilation is more beneficial to me and with this building being right next to a reservoir/country park I want to do my best to keep rodents at bay from using the insulation as bedding. I am going to using breathable membrane on floor, walls and ceilings and it’ll have a number of upvc windows that I’ve bought second hand in good condition to reuse. The floor sheathing material I’m considering opting for is 18mm ext ply treating any cut edges sufficiently, chances are I’ll also give any sides facing the floor a lick of preserver anyway. Is there anything else like for like that’d be a better material for the floor? I’m considering sheeting over the ply in the locations in which animals reside the avoid any water ingress, I considered a thin white catering type plastic that you can buy in 8x4’ sheets at sensible price.

Studwork will be 4x2”, tanalised rails on bottom and top of the studwork all else non tanalised. 1 door external door will be constructing with tanalised timber and cladding with the same cladding as outside, hung using Henderson style sliding runners.

Cladding wise, this is my biggest initial concern I’m going to opt for 120mm x 18mm shiplap cladding from a supplier I’ve bought from for numerous years, I love his stock as it’s solid stuff for the £0.90 a metre. In the past I’ve stapled breathable membrane onto my studs, then screwed on a roof battern which overhangs the shed base then nailed and screwed my cladding to these batterns allowing for any vapour to rise through the air vents high up or for any moisture to fall down past the shed base and go back to natural earth. With this build I’m conscious of having this air gap because of the nature of rodents, I want to avoid giving them a ticket straight in. I’ve considered mesh lining or galv sheeting the base before the plywood to stop any rodents entering from the ground up but I’m conscious I’m not allowing the building to naturally breath. I’m also not 100% that this is the perfect way to clad a shed taking into account moisture control?

Can you guys pass comment please?

Roof material, I’m not certain on as of yet. Was considering rubber for it longevity or shingles, cost dependant at the minute. 2.3m at tall side of the shed and 2.1m at short side. Unsure of overhang at the minute, will probably utilise 4.8m lengths timbers and have quite bit overhangs all around as the weather in the location of the build is often very unpredictable due to height and the exposed location of the property.

Any help or advice you guys can pass on would be much appreciated. Many thanks




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Hi Josh, and welcome.

This is an unusual project, but the principles of the building's construction are covered in the threads linked to in my signature. I don't like timber in contact with the ground, because it automatically limits the life expectancy of the building, but you've done it already, so we just work with what we've got.

You talked about using non-treated timber for the structure. This would be a huge mistake. Around here it is harder to find non-treated structural timber than treated (it's a special order), and treated is virtually the same price as non-treated, so I'm at a loss as to why you'd be planning on doing this. I urge you to reconsider.

Wrapping the structure in a breather membrane before counterbattening and then cladding is an absolute fundamental of making the building work. It will "breath" perfectly well, because that's what this construction is designed to allow. You simply seal the gap at the bottom with a mesh to prevent pests entering. Stainless steel mesh is available on a roll, or if you are lucky you might find thin-coat plaster corner bead made with a fine mesh, and that makes fixing extremely quick and easy. I'd be much more concerned about the void you are creating under the floor, which looks like rodent paradise.

You seem to be saying that you'd have a breather membrane internally. Is that right? Why would you do that? Its function is to keep liquid water one side, but allow water vapour through, and that is not the function you want on the inside of the walls, floor and ceiling. You haven't said what you are planning to use to line the inside of the walls, but it is on the inside that you want a highly impervious material to prevent water vapour getting into the structure. You will also need either diagonal bracing or sheathing, and if you use OSB or ply for the sheathing, internally, you achieve two things with the one layer: racking resistance and vapour resistance. That's why you'll see most workshop builds on this and other forums using OSB lining internally.

Shiplap, in my experience, is seldom treated, which is a pity. Feather-edge board is almost universally treated, and what I normally use. It's the vernacular material in these parts.

Rubber (EPDM) will be hugely cheaper than shingles, unless you are riving the shingles yourself by hand. Avoid the plastic edging strips etc, which cost a fortune and can be designed away normally.

Finally, just a note on planning permission. If you are in a national park, AONB, or World Heritage Site, you'll need permission before building this. If you are in Scotland a different planning regime exists and you should check with your local authority first.
Thank you very much for your informative response, I’ve checked the link in your signature and it’s exactly how I’d clad the building.

Cladding>2x1” batterns>breathable membrane>4x2”.

Internally it will be sheathed with 1/2” ply, in animal areas it’ll probably have a plastic finish, something that commercial catering companies would use to allow for hygienic washable surface.

Tanalised 4x2” worked out at £150 more expensive, my logic for the bottom and top rail of the stud being tanalised was to ensure the vital components that are at risk of water ingress are protected. I know timber supports aren’t ideal but they provide best value for money at the minute, they are treated and they’ve also been painted with creosote and will get a for more licks before postcrete goes in.

Rodent proofing, I was contemplating installing a skin of small diameter weld mesh under the plywood to stop any rodent gnawing that will occur the instant chickens spill feed but I was then worried of the 3/4” ply flooring being all over the place as a result of the weld mesh, my other option was a thin galvanised sheet metal but then I didn’t know if it this would work against the plywood and stop it from breathing and potentially make the wood sweat?

I’ve come across a stainless steel wire 50mm tall that would sit perfectly stapled at the bottom of edge side in between the vertical 2x1” batterns. This would reduce my worry of rodents coming straight through the air gap.

Again, thank you very much for your advice. Let me know what you think.
I'm not 100% sure of your floor build-up, but if it is just ply on joists with nothing on the underside of the joists, then that would be where I'd try to site my rodent-proofing. You could nail some EML on the underside, for instance. I'm always hugely reluctant to put an impermeable layer in a floor, because any spillage inside will just sit there on top of it for years and years, doing all sorts of damage. Not only that, but it is an extremely cold material and surface, so would necessarily be the site of condensation. Thus the idea of a solid sheet of galvanised steel gives me the heeby-jeebies.

Look, spend the extra £150, if that's what it costs (it wouldn't here). The bottom ends of those studs are going to be in the most vulnerable position in the the bottom of the walls. In old buildings it is the sole plate and the bottom ends of the studs which are always rotten, and you could potentially go to all the trouble of building this building and then finding it is rotten in only 2 or 3 years time. You really can spoil a ship for a ha'porth of tar.