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Shed insulation help

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All-Metal

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I have a shed which I want to insulate. I’m going to be using insulation board and my frame is 70mm x 35mm. I’ve been told by my brother in law(who’s an architect)that I need a minimum 50mm air gap on the walls which would mean having to extend the frame which I really don’t want to do. So my options are 50mm board 20mm gap,40mm board 30mm gap or 25mm board 45mm gap. Obviously the thicker the board the better insulation but would the small gap cause me problems somewhere down the line. I definitely don’t want to end up with my shed rotting which he has suggested will happen if not done properly. Also he said that I need to ventilate the air gaps somehow from the outside from the top and the bottom. My sheds got so many different sections that I’d end up with vents all over my shed if I was to do this. Any suggestions or help with this would be great 😊
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Spectric

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Hi

What insulation is in the roof, thats where you will lose a lot of heat and you can get the greater gains.
 

BruceK

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My shed is an ex building site hut which I adapted for a family wedding. It has something similar to Tyvec between the frame and the shiplap exterior. I didn't worry about the air gap & filled the 50mm gap with celotex bought from a seconds outlet & lined the walls on the inside with shuttering plywood. It's insulated under the wooden floor with the same stuff and also under the plywood roof (which I then covered with second hand corrugated iron). It's totally dry and keeps warm with just a little heat (cheap second hand double glazed windows too). As long as your shed is kept damp free by keeping it painted and sealed you should be okay. The lack of air space will only be a dry rot problem if the wood gets wet (68% moisture content or something like that the guy told me). We had a huge problem with it in our old Victorian house but the shed is bone dry. it helps that the shiplap is pressure treated too of course.
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Paul Narramore

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Like to many posts on this forum, I think you are over-thinking your 'problem', over complicating it. Stop listening to too much advice and use your gut instinct. It rarely let's me down.
 

All-Metal

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Like to many posts on this forum, I think you are over-thinking your 'problem', over complicating it. Stop listening to too much advice and use your gut instinct. It rarely let's me down.
So what would your gut instinct be for the insulation and the air gap? Also vents or no vents? Is it not pointless having an air gap if it’s not ventilated?
 

BruceK

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So what would your gut instinct be for the insulation and the air gap? Also vents or no vents? Is it not pointless having an air gap if it’s not ventilated?
If I had a concern about this it would only be regarding dry rot. The dry rot spores like still air so if you do decide to go for an air gap I'd consider some sort of vent somewhere. The trouble is that your frame is likely to have so many different sections and, because your shed is made from t&g which is pretty airtight, you'd need to vent each one to allow air to flow through. Unlike in a brick or stone building, in a wooden shed I'd be tempted to forget the air gap and fill it all in with insulation like I've done with mine. 4 years down the line and there's still no mushroom smell.
 

OldWood

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I'll go with Paul's comment !! I built my workshop 15 years ago as a lean-too to the garage. If I remember rightly I stapled fibreglass insulation to the framing with a nod to an air gap, but with a membrane inside to stop warm damp air getting into the insulation and condensing there. I did similar with the ceiling, though that is going to have be all replaced as rats got in there this past summer and pushed much of that insulation out. Probably go with Kingspan.
Rob
 

Jarno

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Built my own shed last year and spent a significant time learning about insulation and barrier foil to prevent condensation issues.
Indeed from the inside out, plywood or osb, fully closed foil-insulation with no voids anywhere stuff it well - foil with slits to allow moisture to escape- outside (mine is douglas lap planks)
The roof is ply- closed foil- PIR with bitumen, epdm roof attached with contact cement
 

harryc

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As a retro fit stick some battens between the frames and leave yourself at least 25mm gap and Stick some foil backed insulation boards in there. Tape over any gaps with aluminium foil so stop thermal bridging and you will have a vapour impervious structure.
What you are trying to avoid is warm air from your shed penetrating the walls and forming condensation.
As a double guarantee cover the insulation with Osb boards.

simple 😀
 

mikej460

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I agree with HarryC's approach as the better solution. I've used YBS foil insulation when dry lining our old cottage and it works very well and I think it could be your answer. Have a look at this video to show a very basic approach which you could improve using insulation boards.

How to insulate your Garden Shed in 30 minutes with the EcoTec Reflective Insulation - YouTube

Then look here for some useful info. YBS Superquilt is excellent stuff but it is a bit expensive but a much better solution than the EcoTec stuff in the vid, so it depends on your budget. If you already have exposed internal vertical studs you could staple the foil to these, seal with tape then fix counter battens then the insulated boards (tip: if you use any form of foil insulation that has a rock wool type of layer then don't screw the counter battens, nail them otherwise the screws will bind with the insulation like candy floss). I would give some thought to venting though, I think you could do this pretty simply and hide any venting. You would need a simple 'soffit' vent at the bottom of each shed section cut out with a hole saw and hidden by an angled board and one at the roof ridge with insect mess fitted, possibly hidden by a raised ridge). For more information:

Instructional How-To Videos • Superquilt-Insulation.co.uk (superquilt-insulation.co.uk)

Hope this helps but ask away if you need any more advice.
 

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