Afternoon all,

I am about to buy a new house and in the garden is a large shed they’ve been using as a kind of home gym but it’s a pretty knackered single walled Structure. It’s about 10ft by 20ft.

Given we are buying a new pad I’ve not got much cash around so thinking about cheapest option to turn it into a place where old sofa and turbo equipment (I.e. Turbo and old telly) won’t get damp and damaged.

I’m thinking polystyene and plaster boards could work but no experience of doing anything like this. Tips and advice welcome!

Brick?

External insulation has some advantages.
https://www.kingspan.com/gb/en-gb/products/insulation/kingspan-insight/articles-and-advice/how-to-insulate-a-garage-conversion-wall-insulate

A vapour barrier will avoid condensation on a cold brick wall. Condensation can lead to mold and rot.

Cheapest way to keep it dry would be a dessicant based dehumidifer.

I’d be careful about using plasterboard that wasn’t the bathroom stuff in any outdoor structure and even then the weight of it would be an issue for most shed roofs if you want to line that too.

I’d probably go for rockwool in the gaps between battens and line it with thinish ply. Still won;t be that cheap on a building that size though.

Obviously insulating the walls and roof helps but the doors, windows and floors still draw heat away.

What type of floor is it?
Insulating a floor can make a big difference. Just standing on a cold floor is going to make you feel cold.

I added office space to my garage by using Celotex boards. Covered the floor, ceiling and walls with Celotex. Floor is covered with chipboard. I screwed battens to the wall, then fastened the Celotex to the battens.

I could add plasterboard but I don’t see the point. It’s single brink so they will just get damp. I don’t see the point in spending any more cash.

Did this 4 years ago and not had any problems.

It’s a wooden shed. Sounds like it might be cheaper to just rebuild. When I’ve got more funds!

yeah, rebuild properly when the time comes, save the money for doing a proper job, spend the inbetween time planning and saving

ibnchris I am no structural engineer, but I do work from my shed/timber structure which has the same footprint you are talking about. It has an A-frame roof with trusses. It was partially insulated (polystyrene and plasterboarded when we moved into the house. I finished the job and it has been completely fine for me. The windows are single pane and I have simply used a polythene double glazing kit and added insulating tape around the edges. I did partition it to create an office space and a shed space, with a door between. This cuts down the space I need to heat. I did need to create more light so installed double glazed panes into my double doors.

Thanks dogmatix – any idea how much you spent?

Insulation only slows the temperature inside from reaching the same temperature as outside. Unless you’re spending quite a lot of money heating it regularly, I’d guess that insulation will make no difference to the temperature when you get inside, it will just make it faster to warm up / slower to cool down

So for a timber shed, is the correct approach to insulate between the studs but leave an air gap, then a waterproof membrane over it all, then ply/plasterboard line over that?

Asking for a friend.

For our summerhouse, I used the silver ‘bubble wrap’ insulation between the battons – stapled to the walls and roof, then ply lined the lot by screwing into the battons. Cheap option, for a cheap summer house, but it works a treat. Warm in winter, cool in summer. My wife uses it for craft, and has a load of fabric in there – absolutely no damp.

I’d consider using some of this. I used a similar product on my conservatory. The silver rape makes all the difference. It’s also very nice to use compared to traditional wool fibres.

This is a video for the floor, there’s another fir walls but you get the idea

Careful using the foil backed bubblewrap stuff (superfoil) on any building you may want to use as an office. I built a Dunster house chalet thing and insulated it with superfoil. God damned stuff turned it into a faraday cage, within which i could get neither mobile nor wifi signal.

Would that superfoil stuff work as a temporary measure on a UPVC conservatory roof? Can’t afford a warm roof conversion at the moment but it’s **** Baltic in there at the moment.

So for a timber shed, is the correct approach to insulate between the studs but leave an air gap, then a waterproof membrane over it all, then ply/plasterboard line over that?

Depends what your friend means by air gap. For best results wind/waterproof but vapour permeable wrap on outside. Then insulation w/no airgap, or at least not one big enough to allow the warmer air to circulate in it. Than a vapour impermeable wrap on the inside. Then finish interior.

Tri iso or similar stapled to the uprights, 50x38mm battens run horizontally over the top, osb ply to finish.
Wouldn’t use plasterboard and the above is exactly what I did.

@doomanic there’s some good info on this thread.

I finally converted my conservatory

@hot_fiat I never even considered that!

Took me a few reads to realise this thread was not about insulting a shed.

I am disappointed.

Took me a few reads to realise this thread was not about insulting a shed.

Took me till reading your post to realise this wasnt a shed thread!

I just shoved some polystyrene insulation between joists after backing the outside with a waterproof layer then stuck OSB and plywood over.

Some of the polystyene was just packing from (as best I remember) kitchen units and some from Wickes then the window is made from the insulated square section plastic fixed in place with some silicone sealant and panel pins…. Under the floor it has some proper Kingspan

Joists are marked so I can screw in hooks and stuff…

Positives.. cheap (the OSB and ply was most expensive part…) insulates well enough…could be better but diminishing returns. Screwed in so if I do want to insulate better I can always put in some better insulation.

Negatives .. wasps dug out the polystyene and made a nest in the space.

I lined 3.5 walls and the roof with the bubble wrap – one side has glazing and a double door, so no issues with WIFI to the shed – plus if you have electric you could put a mains power line WIFI/CAT5 booster if the signal won’t get that far.

Interested in this thread as need to do something to sort out the condensation on metal garage roof.

It’s a concrete panel garage and the eventual plan is to knock it down and build something nicer but that is way way down the list so looking to do something to stop the rain inside whenever it’s chilly out. I know ideally I’d get a new roof but I don’t have the money for that, was wondering whether sticking some kingspan/celotex to the underside of the roof would help? I know it’s not idea bit would it be an improvement?

Hmm. Line the bottom few feet with plastic sheeting then pour in loads of expanding foam mix. It’ll fill the entire shed. Then you can open the door and chisel out a cavity in the middle, and you’ll be surrounded by insulation. Perfect.

Just hijacking this thread a bit, hopefully for some agreement on the best approach for what I’m hoping to do.

I’ve got to partition off and insulate part of a large wooden outbuilding. It’s a really well-built thing, on a concrete pad and I’m hoping to section-off about a third that will be used as an office. The existing double doors I will replace with modern aluminium glazed doors.

So, was hoping that some here may be able to comment on how best to approach each scenario as I’m a humble wood whittler and an insulation noob.

First off the floor. I was thinking I would lay joists down, then Kingspan type stuff between. Should I then fit a vapour barrier before I put down the chipboard/ply floor, or should the vapour barrier go right down first on the concrete before the joists even?

Next up are the walls. These are simply tongue and grooved cladding over the frame structure. What’s the best approach here? Kingspan/foam board between but not touching the inside face of the T&G, then a vapour barrier, then line? Or do I not need a gap of any sort between the T&G and insulation? Or even, should the vapor barrier be against the T&G, then the insulation and lining?

Finally the roof. It’s just a felt roof with OSB underneath. Same approach as the walls?

Sorry for the noobie questions, but it’s something I’ve not had much experience with and don’t want to make an expensive mistake! 😊👍

Interested in this thread as need to do something to sort out the condensation on metal garage roof.

Had same issue – one garage is done with kingspan – it worked but expensive and time consuming.

did the other garage with twin tank expanding foam insulation.

It was 50 quid more expensive but SUPER quick.

Foil backed PIR, and aluminium tape to seal any gaps.
Not so easy to install on an existing shed, but can be the best option.

The vapour barrier needs to be air / vapour tight if it is to keep the relatively moist air in and away from the walls. Moist air will be drawn through even tiny gaps and then condense on cold walls and lead to damp and mould and rot.

How to insulate your shed: Insulating pricing, materials and expert advice

But a breathable membrane might be needed on the outside.
In winter the walls might get damp, and never get warmed up from the inside because the insulation keeps the heat in, so the membrane keeps the water off.

Cheers Paton, but that dude is building onto a timber suspended floor. Are you saying use the same approach for over a concrete pad?

On an existing concrete floor anything you do will raise the floor height, and reduce the headroom. So your options are limited.

The technique and info that the dude is using applies more to the walls and roof.

Insulating anything like this is about understanding how the reduction of heat and ventilation to some of the structure is going to affect where condensation will form, and what the longer term impacts of that condensation will be.

Kayak, your concrete floor doesn’t need batons, nearly all PIR board is weight bearing, but you do need decent board ontop. DPM down,to stop moisture off the concrete, PIR down, seal the top joints, then lay 22mm chip board tongue and groove or 18mm ply. You underlying DPM should come up above the floor level in order to meet/join the wall barrier.

If you insulate the walls with PIR right up against the cladding, you risk the timber not being adequately ventilated on its back side, so it should really stand off. This might not be a problem depending on how much weather the wall gets, but how do you know? It would be quickest and most effective for heat retention to bash PIR boards straight across the internal frame and then board over, but you will loose interior space with this method.

Everything else is a compromise somewhere along the line, such as cutting and filling between frame members and then over boarding, which leaves more cold bridges but takes less of the internal space.

On an existing concrete floor anything you do will raise the floor height, and reduce the headroom. So your options are limited.

Not really an issue. It’s a pitched roof so pretty tall. I imagine I could lose 50-100mm no worries on the floor.

Kayak, your concrete floor doesn’t need batons, nearly all PIR board is weight bearing,

Cheers. I hadn’t realised that until now. Just watched a Restoration couple youtube that shows it quite well.

Its really the door height and if the door opens inwards that you will notice if you raise the floor height.