Insulating summerhouse (during build)

[Stringman_uk]

Mr Rusty
Thanks for your reply.
I have cut the timber for the frame based on a 25mm over hang of the base so that the centre of the 4x2 sits on the frame, so add on the battens and cladding and the overhang is about 60mm , Do you see a problem with this?

I was hoping to avoid sheathing the frame and have actually "designed" it to be 2 structures that will be bolted together I was going to use builders straps and lots of noggins. If that doesnt work then it will have to be sheathed.
What would you advise to seal the raw edges.
Thanks for the links I will investigate.

I also did a quick search for the membranes as I only really need 15m x 2.2 and saw these: though I am a bit dubious

Capital Valley Plastics Ltd Vapour Barrier Green 300ga 20m x 2.5m - Screwfix

Rhinovent Ultra Breathable Membrane Classic 1 x 50m | Toolstation

• BBA certified medium weight breathable roof tile underlay • Suitable for warm and cold roof applications • Requires no ventilation if installed in accordance with instructions

www.toolstation.com

Any thoughts?
I also see there are few sellers on ebay selling tyvek by the metre which could work out reasonable

 

[mrrusty]

Last first - seal the floor edge with anything - paint, silicon, PU glue - whatever you have left over. it's only a bit of protection.

For a framed wall the 4x2 would normally be the other way round making the wall 4" thick not 2. The sheathing gives the whole thing rigidity making a box section. A 4x2 frame, sheathed with the fixings every 250mm or so is incredibly stiff and resists deforming and racking under load. Sheathing is quite cheap - you could use 9mm osb or even 5mm ply - it's a lot faster and simpler to fix a panel over a frame than to fit a load of noggins and diagonals (and without either diagonals or sheathing you risk racking and lozenging of the frame - I guess you mean to use the straps as diagonals? - should be OK but I'd use sheathing because it contains the insulation as well).

A 60mm overhang is OK but if your 4 x 2's are side on with 25mm overhang and 25mm bearing (in reality probably more like 22mm as 4x2 is more like 95x45) the bearing is a bit narrow but more than likely OK in this application. Personally I would sit the frame flush and overhang just the battens for the cladding. The membrane can also overhang the base frame protecting both the frame and floor edge from secondary penetration should there be any.

 

[Stringman_uk]

Last first - seal the floor edge with anything - paint, silicon, PU glue - whatever you have left over. it's only a bit of protection.

ok, so noneed to wrap it in wpm ( I have loads left over

For a framed wall the 4x2 would normally be the other way round making the wall 4" thick not 2.

Maybe i didnt explain very well it the base of the frame will be sitting in the 4" part ( so the wall will be 4" thick)

The sheathing gives the whole thing rigidity making a box section. A 4x2 frame, sheathed with the fixings every 250mm or so is incredibly stiff and resists deforming and racking under load. Sheathing is quite cheap - you could use 9mm osb or even 5mm ply - it's a lot faster and simpler to fix a panel over a frame than to fit a load of noggins and diagonals (and without either diagonals or sheathing you risk racking and lozenging of the frame

Not sure what that is

- I guess you mean to use the straps as diagonals? - should be OK but I'd use sheathing because it contains the insulation as well).

maybe I will look at the costs

A 60mm overhang is OK but if your 4 x 2's are side on with 25mm overhang and 25mm bearing (in reality probably more like 22mm as 4x2 is more like 95x45) the bearing is a bit narrow but more than likely OK in this application. Personally I would sit the frame flush and overhang just the battens for the cladding. The membrane can also overhang the base frame protecting both the frame and floor edge from secondary penetration should there be any.

That makes sense . I guess there is no hard and fast rule.
I will make it flush but may have an overhang at the back for cable entry

 

[Stringman_uk]

So your framing up over a floor on a base. Yes, arrange it so that the cladding overhangs the edge of the floor, and yes, it is always a good idea to seal the raw edge of the flooring. The framing can be flush with the floor edge, but the battens under the cladding will allow it to overhang. I presume you are going to sheath the outside of the frame in thin OSB? in which case over that will go a breathable membrane. I recently used https://www.cwberry.com/protect-tf200-vapour-permeable-membrane which is a bit cheaper than tyvek and perfectly good enough for a summerhouse. This outer membrane on the cold side must be breathable. Over that goes battens to form a ventilation space, over that goes the decorative cladding.

Internally, assuming you have insulation in the framing a vapour control layer goes over the framing and under the internal finish. The vapour impermeable barrier stops warm room air getting in to the cold wall and causing condensation. https://www.cwberry.com/125mu-vapour-control-layer-27m-x-50m-green

For a fairly inexpensive and maintenance free cladding (particularly on external walls you can't see) painted metal is not expensive. https://www.cladco.co.uk/sheets/32-1000-box-profile-0-5-thick-polyester-paint-coated-roof-sheet they call them roofing sheets, but they work just as well on exterior walls. You can order them cut to length (because they are a PITA to hand cut). Shop around because different suppliers of cladco have different delivery charges. I have recently used https://www.roofingoutlet.co.uk/col...0-box-profile-sheeting-polyester-paint-coated

Mrrusty
thanks for all your help,
I ended up going with tyvek house rap as it was only about £15 more and I reckon it will be easier to sell on ebay.

 

[Stringman_uk]

Sorry to keep going off on tangents. So the tyvek is bought, the epdm is bought and I have accepted the need to sheath the shed. I am awaiting prices but it looks like osb is the way to go, and it looks like 11mm is only £1-2 more per sheet so I will probably go with that.
So the next niggle I have encountered is the foundations. Or more importantly how to hide them.
Due to the uneven ground the lowest is 7cm above the ground with the highest being 20cm.
I intend to drop the cladding below the frame leaving a breather gap ( covered in mesh) but that leaves the foundations exposed so I wondered if I could drop and cut the sheathing so its about 5cm above the ground by the foundations ( obviously the gaps between the foundations would be cut back to the frame for the breather space) then tyvek wrap, batten and clad, with an extra piece put on across the face of the foundation.

Or a simpler way would to put all the sheathing on as per normal and just add some battens by the foundation and add the extra cladding on those?

 

[Stringman_uk]

Quick question again
I have insulated the walls with the following ( outside in_
shiplap
batten (25mm gap)
Tyvek
11mm osb
4" x 2"
Pir ( with 25mm gap)
vapour membrane
claddinng

with the ceiling its mauch the same
Epdm
18mm osb
6"x 2"
Pir (with 25mm gap)

should I also put the membrane on the ceiling before I put the cladding on the ceiling?

Thanks

 

[motorbiking]

No need for membrane anywhere. But it does depend how you will seal the roof ends? Are you venting the 25mm gap?

 

[Stringman_uk]

No need for membrane anywhere. But it does depend how you will seal the roof ends? Are you venting the 25mm gap?

yes there is a gap front and back for venting

 

[motorbiking]

As long as your PIR is flush with the ceiling and well sealed it doesn't need membrane.

 

[robinbanks]

If it were mine I'd do

shiplap
25mm batten with air between
Tyvek housewrap
11mm osb
4" x 2" with PIR between filling the pockets
25mm PIR with taped joints
25mm batten with air between (for services/cables)
cladding

Epdm
18mm osb
6"x 2" with PIR between filling the pockets
25mm PIR with taped joints
25mm batten with air between (for services/cables)
cladding


If there were tricky details not easy to form PIR around, or reasons why they're might be gaps in the PIR I'd use a membrane on those. Doesn't have to be anything special, even visqueen would do

 

[Stringman_uk]

I ended up membraning the walls and taping every joint on the ceiling.
Thanks all