New wooden workshop - insulation, ventilation and finishing

[JimDiGritz]

Hi,

So I've just ordered two 18x8 ft wooden workshops. They are framed with 38mm x 64mm with 16mm T&G cladding. All timber has been pressure treated & tanalised.

One will be a proper workshop/storage building and the other will be a spare room/study.

I've got a million questions and some answers which I'd love to have sanity checked!!!

I'll start from the bottom!

FOUNDATIONS
I've got a 40x10ft area of hardstanding/concrete. It's at least 30 years old and one of the slabs is not level. I've got a local builder to come in and resurface and level the concrete. This should be ready a few days before the workshops arrive on site !!! :shock:
I don't think there is anything I need to do here...

BASE
The workshops come with floors and I'll need some way of lifting them off the concrete to stop damp. I've heard people using paving slabs, sleepers or concrete piers. What's the best option here?
I'm also concerned about the wind lifting the workshops, it gets pretty windy here.
I'm confused about DPM.. should I put some DPM under the floor joists and the (sleeper, paving slab) base?

WALL INSULATION
I was planning on doing the following to ensure I had sufficient year round insulation (see wall image attached) I've gone ahead and ordered:

DuPontTM Tyvek® Housewrap Vapour-Permeable Timber Frame Wall Membrane - can't do link
SuperFOIL SFTV1L 20 m Thermal and Vapour Barrier for Roofs, Walls and Floors - can't do link

I'm also looking at some cheap 25mm Kingspan/Celotex insulation panels.

Does this make sense? Do I need to treat the inside of the cladding before I insulate? What about caulking or sealing any gaps?

FLOOR INSULATION
I was considering wedging some Kingspan/Celotex insulation panels underneath - between the floor joists.. for the sake of doing the job right do I also need vapour and or breather membranes?

ROOF INSULATION
I'm probably going to do the same as I have for the walls.. unless I'm missing something!

PAINT/TREATMENT
The timber is pressure treated & tanalised and I believe has water proof (Aquashield?).

Before I put the insulation in should I do anything to the inside of the cladding?

I'm planning on painting the exterior in the summer (in six months)

VENTILATION
I'm confused here. I know I'll need ventilation when the workshops are not in use, should I just install some basic Louvre Vents?

WINDOWS
This is a problem area, I've got no windows in the workshop (for security) and the study building has 4 reasonably large single glazed opening windows.

I'm thinking of screwing sheets of perspex on the inside of the window frames to create a poor mans double glazing. I'll also get some think curtains.

Are there any thoughts on blocking drafts around the wooden frame?

DOORS
I've not seen any information on how to insulate a door. I'll have two wooden 4ft double doors.

Rubber sealing strips around edges? What about actual insulation? Should I add framework so I can add insulation??

Cheers

 

[RobinBHM]

Im not sure where you are aiming to position the tyvek housewrap.

I would have an air gap between cladding and insulation

 

[JimDiGritz]

Im not sure where you are aiming to position the tyvek housewrap.

I would have an air gap between cladding and insulation

Isn't that the breather membrane? Inside the cladding and in front of the Kingspan???

 

[Roughcut]

Im not sure where you are aiming to position the tyvek housewrap.

I would have an air gap between cladding and insulation

Isn't that the breather membrane? Inside the cladding and in front of the Kingspan???

As you have said you are buying the timber sheds I assume they will come in Kit form (floor, wall panels and roof) ready for assembly on site.
This will most likely mean the cladding will already be fixed to the stud walls.
Which will mean no air gap between cladding and studding, and no way of positioning the breather membrane in between.
Here's a good example of how timber framed buildings are constructed:
build-a-shed-mike-s-way-t39389.html

 

[JimDiGritz]

Im not sure where you are aiming to position the tyvek housewrap.

I would have an air gap between cladding and insulation

Isn't that the breather membrane? Inside the cladding and in front of the Kingspan???

As you have said you are buying the timber sheds I assume they will come in Kit form (floor, wall panels and roof) ready for assembly on site.
This will most likely mean the cladding will already be fixed to the stud walls.
Which will mean no air gap between cladding and studding, and no way of positioning the breather membrane in between.
Here's a good example of how timber framed buildings are constructed:
build-a-shed-mike-s-way-t39389.html

Yes, I believe the studs and cladding will arrive pre-assembled.

I thought that the breather membrane sat directly inside the cladding, and therefore I could cut widths to fit between the studs...

Have I just wasted £100???

 

[Zeddedhed]

The membrane is normally wrapped around the outside of the studs and stapled on prior to the cladding. I suppose you could cut it into strips and put it between the studs. Lot of hassle though.

 

[xraymtb]

Any reason it couldn't be put in place from the inside and brought out and around each stud? Kind of on the inside but pushed back into each opening

 

[Zeddedhed]

Only that the studs would not be offered the protection of the membrane. If they're treated and the cladding is also you'll get away with it probably, but who knows how long for?

 

[Paul200]

I'm doing something similar to a cheap and nasty shed. My membrane is stapled to the back (or inside) of the framing timbers - but in my case they are only 40mm deep - not 64mm. Then I'm building another stud frame inside that which is 50mm deep and the insulation goes in that. This gives me an air gap between the exterior cladding and the breather membrane.

I did consider your suggestion of pushing the membrane into the frame against the back of the cladding Jim - but I think that air gap is too important. Whatever you do don't forget that the overlap of the membrane is reversed when installed from inside! (Not that I'd make that mistake - never! :? :wink: )

 

[Paul200]

Just found this on another forum - http://www.rmweb.co.uk/community/upload ... 373191.jpg - perhaps it may be helpful. Not a bad idea I thought.

 

[RobinBHM]

The tyvek housewrap is normally fitted on top of the studwork, then tile battens are fitted vertically then cladding horizontally. The bottom of the tile battens is open to the outside allowing ventilation and any rainwater to escape.

I'm not sure there is any gain in fitting tyvek in between the studwork as it isnt protecting the studwork frame and it isnt acting as a breathable membrane as there will a foil barrier behind it as part of the celetex PIR insulation.

Tyvek housewrap is a great barrier, but its like using the thinnest, most crisp wrapping paper you can buy.

I would leave out the tyvek, fit small battens either side of the studs set back by the thickness of the insulation, cut the insulation in between, foam / silicone any gaps. Then use silver tape over the studs showing to complete the foil vapour barrier and then attach your inner finish boarding, or fit a vapour barrier separately.

I always wonder how vapour barriers in sheds work as an unheated space wont always be warmer inside than outside. I suppose the key is to stop any moisture getting into the wall fro either inside or outside.