Summer house - better to insulate or thicker walls?

Miss_Riot

Doozergirl said:

FreeBear said:

ThisIsWeird said:

Tbh, I have no idea how timber rates as an insulator compared to, for example, PIR (rigid, foil-faced insulation board such as Celotex). I imagine timber is 'pretty good', but going even for the thicker timber walls - say 45mm - ain't going to be good enough on its own.

So, since additional insulation will be needed, I think it makes sense to just go for the thinner 18mm timber walls, and line the inside with at least 2", ideally more, of PIR.

Wood is not a very good insulator at ~0.13W/mK compared to PIR at 0.023W/mK (the lower the number, the better). Your 2" (50mm) will be less than half of what would be required for a decent wall, and a third for a roof or floor. Yes, 50mm will provide some insulation, but no where near enough for building regulation compliance. Even although this room isn't going to be used for sleeping, it is worth aiming for BR compliance or better - To do so will reduce heating/cooling costs and make the space much more comfortable.

This.   Also remember that a small timber building has a huge ratio of surface area to volume; in winter it's surrounded by cold air on the top, sides and bottom and would need more heat than an equivalent room in a house.  

And if it's a slot-together job, it's full of air gaps.  You may as well be outside.  

I took shelter in a garden building at the Chelsea Flower Show during a storm and the woman was trying to tell me that the wood in their £10k timber-only building was insulating when the whole thing was hundreds of pieces slotted together. It would have leaked warm air like a sieve.  

Timber has nothing like thermal mass that will retain some heat, unlike a brick/concrete/stone house (even without insulation) 

People should be thinking of their garden rooms like extensions.  They're not cheap even when they're incapable of standing the test of time so it is worth trying to meet the building regulations - with a building regs completion certificate you create peace of mind and a true extension that adds genuine value to a house. 

You need decent structure, minimal air gaps and proper research into the genuine insulation level.  Simply referring to something as 'fully insulated' is a con.  

There's some info on this website which (as freebear recommends),  properly designs rooms from the outset and can meet regs.  
https://www.gloriousgardenrooms.co.uk/built-to-last/

(It's not my company anymore so I'm not advertising myself!)

Our issue is that because I am disabled and we are on one income (the reason my partner needs to work from home) we are on a very limited budget. It's not our house so we can't start doing anything that will require planning permission. We are also not looking to stay here forever as this house doesn't suit our needs but we won't be reassessed for at least a year minimum, and could be on the waiting list many more after that. Hence going for the timber route - we could take it with us. Tbh, I did even consider cob and straw bale but I think the housing association would have been even less likely to be ok with that than a what is essentially a large shed, when they have allowed next door to have a large conservatory on the back of their house for exactly the same reasons. 

FreeBear

Miss_Riot said:

Doozergirl said:

FreeBear said:

ThisIsWeird said:

Tbh, I have no idea how timber rates as an insulator compared to, for example, PIR (rigid, foil-faced insulation board such as Celotex). I imagine timber is 'pretty good', but going even for the thicker timber walls - say 45mm - ain't going to be good enough on its own.

So, since additional insulation will be needed, I think it makes sense to just go for the thinner 18mm timber walls, and line the inside with at least 2", ideally more, of PIR.

Wood is not a very good insulator at ~0.13W/mK compared to PIR at 0.023W/mK (the lower the number, the better). Your 2" (50mm) will be less than half of what would be required for a decent wall, and a third for a roof or floor. Yes, 50mm will provide some insulation, but no where near enough for building regulation compliance. Even although this room isn't going to be used for sleeping, it is worth aiming for BR compliance or better - To do so will reduce heating/cooling costs and make the space much more comfortable.

This.   Also remember that a small timber building has a huge ratio of surface area to volume; in winter it's surrounded by cold air on the top, sides and bottom and would need more heat than an equivalent room in a house.  

And if it's a slot-together job, it's full of air gaps.  You may as well be outside.  

I took shelter in a garden building at the Chelsea Flower Show during a storm and the woman was trying to tell me that the wood in their £10k timber-only building was insulating when the whole thing was hundreds of pieces slotted together. It would have leaked warm air like a sieve.  

Timber has nothing like thermal mass that will retain some heat, unlike a brick/concrete/stone house (even without insulation) 

People should be thinking of their garden rooms like extensions.  They're not cheap even when they're incapable of standing the test of time so it is worth trying to meet the building regulations - with a building regs completion certificate you create peace of mind and a true extension that adds genuine value to a house. 

You need decent structure, minimal air gaps and proper research into the genuine insulation level.  Simply referring to something as 'fully insulated' is a con.  

There's some info on this website which (as freebear recommends),  properly designs rooms from the outset and can meet regs.  
https://www.gloriousgardenrooms.co.uk/built-to-last/

(It's not my company anymore so I'm not advertising myself!)

Our issue is that because I am disabled and we are on one income (the reason my partner needs to work from home) we are on a very limited budget. It's not our house so we can't start doing anything that will require planning permission. We are also not looking to stay here forever as this house doesn't suit our needs

Something that bolts together rather than "built on site" would be ideal then. I would suggest using ground screws to support the floor rather than having a concrete base put down - Ground screws can be removed with relative ease unlike a concrete base, so that would keep the HA happy.. They might not be so keen on having a power cable installed (it would need to be armoured cable buried in the ground to a depth of around 750mm).

ThisIsWeird

Can I ask what your budget is, MissR? And will any of it be DIYed?

MikeJXE

Regarding insulation thickness I suggest you take a look at building regs for a brick and tile house. 150mm under under floors, 150mm between 2 100mm brick/block walls, 280mm in roof.

If you think a couple of inches in a 18mm thick wooden skin will be adequate then expect a very large heating bill. 

Doozergirl

Miss_Riot said:

Doozergirl said:

FreeBear said:

ThisIsWeird said:

Tbh, I have no idea how timber rates as an insulator compared to, for example, PIR (rigid, foil-faced insulation board such as Celotex). I imagine timber is 'pretty good', but going even for the thicker timber walls - say 45mm - ain't going to be good enough on its own.

So, since additional insulation will be needed, I think it makes sense to just go for the thinner 18mm timber walls, and line the inside with at least 2", ideally more, of PIR.

Wood is not a very good insulator at ~0.13W/mK compared to PIR at 0.023W/mK (the lower the number, the better). Your 2" (50mm) will be less than half of what would be required for a decent wall, and a third for a roof or floor. Yes, 50mm will provide some insulation, but no where near enough for building regulation compliance. Even although this room isn't going to be used for sleeping, it is worth aiming for BR compliance or better - To do so will reduce heating/cooling costs and make the space much more comfortable.

This.   Also remember that a small timber building has a huge ratio of surface area to volume; in winter it's surrounded by cold air on the top, sides and bottom and would need more heat than an equivalent room in a house.  

And if it's a slot-together job, it's full of air gaps.  You may as well be outside.  

I took shelter in a garden building at the Chelsea Flower Show during a storm and the woman was trying to tell me that the wood in their £10k timber-only building was insulating when the whole thing was hundreds of pieces slotted together. It would have leaked warm air like a sieve.  

Timber has nothing like thermal mass that will retain some heat, unlike a brick/concrete/stone house (even without insulation) 

People should be thinking of their garden rooms like extensions.  They're not cheap even when they're incapable of standing the test of time so it is worth trying to meet the building regulations - with a building regs completion certificate you create peace of mind and a true extension that adds genuine value to a house. 

You need decent structure, minimal air gaps and proper research into the genuine insulation level.  Simply referring to something as 'fully insulated' is a con.  

There's some info on this website which (as freebear recommends),  properly designs rooms from the outset and can meet regs.  
https://www.gloriousgardenrooms.co.uk/built-to-last/

(It's not my company anymore so I'm not advertising myself!)

Our issue is that because I am disabled and we are on one income (the reason my partner needs to work from home) we are on a very limited budget. It's not our house so we can't start doing anything that will require planning permission. We are also not looking to stay here forever as this house doesn't suit our needs but we won't be reassessed for at least a year minimum, and could be on the waiting list many more after that. Hence going for the timber route - we could take it with us. Tbh, I did even consider cob and straw bale but I think the housing association would have been even less likely to be ok with that than a what is essentially a large shed, when they have allowed next door to have a large conservatory on the back of their house for exactly the same reasons. 

Permitted development rights (ie.  Planning permission) are based around the size and use of a building, not whether it is fit for purpose or the materials it is built from.  Garden offices fall under the same planning rules as sheds.  

You haven't said what your budget is but if it is so low that it's not worth investing in something fit for purpose then, frankly speaking, it isn't really worth investing in at all.  You need to be very careful about what you buy and your expectations from it.  

Doozergirl

Oh, and proper houses can and are built from timber (I linked you to a company that only sells timber garden rooms) but there is a huge difference in quality between a shed and a house, right?  

ThisIsWeird

Not pretty, but from a quick look at my (across the water) 'local' Fb Marketplace: https://www.facebook.com/marketplace/item/199040503118886/?

ThisIsWeird

https://www.facebook.com/marketplace/item/186583450855832/?

Dead easy to line with 2" or 3" (nuts to go more) PIR.

Miss_Riot

ThisIsWeird said:

Can I ask what your budget is, MissR? And will any of it be DIYed?

Looking to keep it under 5k

Miss_Riot

MikeJXE said:

Regarding insulation thickness I suggest you take a look at building regs for a brick and tile house. 150mm under under floors, 150mm between 2 100mm brick/block walls, 280mm in roof.

If you think a couple of inches in a 18mm thick wooden skin will be adequate then expect a very large heating bill

As much as we would like to spend more we don't have it to spend and couldn't get it on finance. I need my partner at home to help me recover from up coming surgery which is likely to be a lengthy recovery but he also needs to still be working because UC isn't enough to live on it's own. We don't have many other options. Our living room isn't big enough for a desk and his job requires 2 monitors so it would need to be a big desk. We aren't going to be staying there for more than 3/4 years, we can't take bricks with us. They also wouldn't agree to anything that is "permanent" they have already told me this. We don't have many options.