Insulating Summerhouse with Celotex
Discussion
After a lot of googling I'm getting rather confused, so hoping I can be set straight...
I have a summerhouse I'm using as a gym and over the winter its cost a small fortune to heat, even just to keep it above 5 degrees. I'm therefore planning on insulating it where possible without going OTT.
I've decided on celotex for walls and roof and secondary glazing for the windows/doors. But I am reading conflicting advice on what's required. Remember, this is only a glorified shed so I really don't want to throw thousands at it.
Most advice seems to suggest filling the gaps between the battens with celotex (5cm as that's the full depth of the battens) then fixing some 6mm or so ply over the top. Also suggested to fix a vent or two or use a dehumidifier. I'm good with this.
But, other advice is that a damp proof membrane is needed on the cold side. Some say it is, some say it isn't. As i don't fancy removing the current wall, I'm not sure how I'd fix this, assuming it is even required.
Others say I should not pack the celotex to the full depth of the battens and that an air gap should be left between the celotex and the outer wood. If so I'd need to use thinner celetex and mount it on thin battens to give the gap. Bit more of a pain but ok. Now some say I need air holes for circulation, especially in the roof void. Not sure how I can do that as the summerhouse construction has wooden battens going around to top so I've nowhere to drill the holes.
Am I overthinking this?!! Would my original plan of stuffing gaps with celotex and overcladding with ply, and being mindful of airflow be good enough?
Some clarification would really be most appreciated!
I have a summerhouse I'm using as a gym and over the winter its cost a small fortune to heat, even just to keep it above 5 degrees. I'm therefore planning on insulating it where possible without going OTT.
I've decided on celotex for walls and roof and secondary glazing for the windows/doors. But I am reading conflicting advice on what's required. Remember, this is only a glorified shed so I really don't want to throw thousands at it.
Most advice seems to suggest filling the gaps between the battens with celotex (5cm as that's the full depth of the battens) then fixing some 6mm or so ply over the top. Also suggested to fix a vent or two or use a dehumidifier. I'm good with this.
But, other advice is that a damp proof membrane is needed on the cold side. Some say it is, some say it isn't. As i don't fancy removing the current wall, I'm not sure how I'd fix this, assuming it is even required.
Others say I should not pack the celotex to the full depth of the battens and that an air gap should be left between the celotex and the outer wood. If so I'd need to use thinner celetex and mount it on thin battens to give the gap. Bit more of a pain but ok. Now some say I need air holes for circulation, especially in the roof void. Not sure how I can do that as the summerhouse construction has wooden battens going around to top so I've nowhere to drill the holes.
Am I overthinking this?!! Would my original plan of stuffing gaps with celotex and overcladding with ply, and being mindful of airflow be good enough?
Some clarification would really be most appreciated!
sfella said:
Personally I would leave an air gap, so rather than 50mm of celotex I would use 35 or 40mm if you can get it. A breathable membrane would also be worth considering to help prevent a build of moisture. Shouldn't cost too much to do
Thanks for the reply. If I was to leave a gap, I assume it should be on the outside (ie: between insulation and outer skin)? Would I need to air the void?I think in this instance filling the full depth between the battens will be fine, with the ply over the top: It's not like a house where it's occupied nearly 24/7 with all the attendant moisture build up, showers, drying washing, cooking, people wanting to breathe etc. Vapour barriers/interstitial condensation and air gaps are, as you allude to, over thinking it for a summerhouse.
page3 said:
If I was to leave a gap, I assume it should be on the outside (ie: between insulation and outer skin)? Would I need to air the void?
Yes, if you leave an air gap, you would need to cross-ventilate the void above the insulation (ie. eaves and ridge) for it to be effective, which is probably going to be difficult to achieve, since the design of the summer hoouse roof won't have been intended to accommodate it.For this reason, I'd be inclined to push the Celotex tight up to the underside of the roof.
You should really then be fitting a 'vapour barrier' (lapped and taped polythene, basically) on the WARM (ceiling) side of the insulation to pref=vent interstitial condensation.
Whether you do, or whether this represents 'over thinking', as Wolfracesonic suggests, depends on how cautious you want to be and the pattern of usage of the building. Unless you're doing stuff in there that generates a lot of moisture (cooking, boiling kettles, bath, shower), then you will probably get away with it, as the basic structure of the building will be leaky enough to disperse most of the moisture you're putting into the air.
Really appreciate all the advice 
If i'm not leaving a gap, I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
If I do leave a gap, as mentioned above it will be difficult to vent as the summerhouse design doesn't really allow for it.
I did consider the bubble wrap type stuff, but that really does need a gap to work and I didn't think the finished product looks as good.
The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
If i'm not leaving a gap, I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
If I do leave a gap, as mentioned above it will be difficult to vent as the summerhouse design doesn't really allow for it.
I did consider the bubble wrap type stuff, but that really does need a gap to work and I didn't think the finished product looks as good.
The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
page3 said:
Really appreciate all the advice
If i'm not leaving a gap, I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
If I do leave a gap, as mentioned above it will be difficult to vent as the summerhouse design doesn't really allow for it.
I did consider the bubble wrap type stuff, but that really does need a gap to work and I didn't think the finished product looks as good.
The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
50mm won't be a problem. The real problem is damp, so you'll need ventilation. Cut a hole through the walls to allow a a couple of vents, one high the other low, this sort of thingIf i'm not leaving a gap, I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
If I do leave a gap, as mentioned above it will be difficult to vent as the summerhouse design doesn't really allow for it.
I did consider the bubble wrap type stuff, but that really does need a gap to work and I didn't think the finished product looks as good.
The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
http://www.ebay.co.uk/itm/6-x-3-White-Plastic-Adju...
Then add a small bathroom sized extractor fan for when you are using the room.
S6PNJ said:
page3 said:
I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
Hi OP, where are you planning to buy your Celotex from as I'm currently pricing up some internal insulation as well and am always on the lookout for other suppliers.S6PNJ said:
Hi OP, where are you planning to buy your Celotex from as I'm currently pricing up some internal insulation as well and am always on the lookout for other suppliers.
Cheapest place I've found so far is (surprisingly) Wickes for both 50mm and 25mm as their prices include delivery, which is often pricey. page3 said:
Really appreciate all the advice
The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
Are you trying to keep it warm 24/7 seven days a week?The room is only used 3 to 4 times a week for a gym. I had the roof redone last autumn (with rubber) but with no insulation at all it's been 0 to 2 deg C even with an oil filled radiator on. It also doubled my household electricity usage in December to February! It doesn't need to be overly warm, but I want to protect the machinery and cold slippery Kettlebells are a danger to use!
I've got a large summer house (5m x 4m) which is insulated along the lines of your thinking and I've got a 2kw fan heater in there.
Even when it's been freezing outside it's only taken a couple of hours to get it up to a comfortable temp.
Squiggs said:
Are you trying to keep it warm 24/7 seven days a week?
I've got a large summer house (5m x 4m) which is insulated along the lines of your thinking and I've got a 2kw fan heater in there.
Even when it's been freezing outside it's only taken a couple of hours to get it up to a comfortable temp.
My summerhouse is 3 x 4 split in to two rooms, the front is my gym the back an extra shed/workshop. I had power, lighting and network installed last year. I also had the crappy felt roof replaced with rubber.I've got a large summer house (5m x 4m) which is insulated along the lines of your thinking and I've got a 2kw fan heater in there.
Even when it's been freezing outside it's only taken a couple of hours to get it up to a comfortable temp.
The idea is to make this a nice place to be to encourage me to use the gym and try to obtain some level of fitness. I'm impressed with myself that I've used it right through the winter period!
It only needs to be kept above freezing (say 5 deg) to protect the machinery and hifi etc. When I'm using the room I'd then warm it a bit more. This winter was the first time I've been using it as a gym and I have a 500 watt heater and dehumidifier in there. The two things I found were:
1. With the oil radiator on low thermostat setting 24/7 I used double the electricity in December, Jan and Feb than I usually do for the whole house.
2. When heated from say 2 C to 12 things like the kettlebells wouldn't be usable as too cold and slippery.
Without spending a fortune, my plan is:
50mm celotex within the battens on walls and roof. Over clad with ply.
Secondary glazing for the three large windows and two doors.
Vents high and low both ends.
Extractor fan.
New rubber floor matting. Good for insulation and gym use.
Hoping to do the whole lot for around £500 or so which will pay for itself in two years.
roofer said:
S6PNJ said:
page3 said:
I thought I might as well use 50mm as I've room for it and it's not a lot more expensive.
Hi OP, where are you planning to buy your Celotex from as I'm currently pricing up some internal insulation as well and am always on the lookout for other suppliers.page3 said:
My summerhouse is 3 x 4 split in to two rooms, the front is my gym the back an extra shed/workshop. I had power, lighting and network installed last year. I also had the crappy felt roof replaced with rubber.
The idea is to make this a nice place to be to encourage me to use the gym and try to obtain some level of fitness. I'm impressed with myself that I've used it right through the winter period!
It only needs to be kept above freezing (say 5 deg) to protect the machinery and hifi etc. When I'm using the room I'd then warm it a bit more. This winter was the first time I've been using it as a gym and I have a 500 watt heater and dehumidifier in there. The two things I found were:
1. With the oil radiator on low thermostat setting 24/7 I used double the electricity in December, Jan and Feb than I usually do for the whole house.
2. When heated from say 2 C to 12 things like the kettlebells wouldn't be usable as too cold and slippery.
Without spending a fortune, my plan is:
50mm celotex within the battens on walls and roof. Over clad with ply.
Secondary glazing for the three large windows and two doors.
Vents high and low both ends.
Extractor fan.
New rubber floor matting. Good for insulation and gym use.
Hoping to do the whole lot for around £500 or so which will pay for itself in two years.
Once you insulate it get a fan heater.The idea is to make this a nice place to be to encourage me to use the gym and try to obtain some level of fitness. I'm impressed with myself that I've used it right through the winter period!
It only needs to be kept above freezing (say 5 deg) to protect the machinery and hifi etc. When I'm using the room I'd then warm it a bit more. This winter was the first time I've been using it as a gym and I have a 500 watt heater and dehumidifier in there. The two things I found were:
1. With the oil radiator on low thermostat setting 24/7 I used double the electricity in December, Jan and Feb than I usually do for the whole house.
2. When heated from say 2 C to 12 things like the kettlebells wouldn't be usable as too cold and slippery.
Without spending a fortune, my plan is:
50mm celotex within the battens on walls and roof. Over clad with ply.
Secondary glazing for the three large windows and two doors.
Vents high and low both ends.
Extractor fan.
New rubber floor matting. Good for insulation and gym use.
Hoping to do the whole lot for around £500 or so which will pay for itself in two years.
Your 500w rad might keep it frost free .... but only if you leave it on 24/7.
Through the winter my heater 2kw floor standing fan heater only needed to be on for a couple of hours to get it up to about 17 degs - turn it down to 1kw while I'm out there (for a couple of hrs) and it might reach 20 degs.
Turn it off - and 20hrs or so later (whilst leaving a widow slightly open for ventilation) it might be freezing outside but still 7 degs inside. A further 2 hrs of 2kw fan assisted heat and it's back up to 17 degs - turn it down to 1k and within another 2hrs it's at 20 degs
Heat rises - so at the moment the heat from your rad is instantly rising, going straight to the ceiling and out through your uninsulated roof.
A fan assisted heater keeps the heat moving around the room so (once you're draft proof) everywhere and everything warms up a lot more quickly and evenly - and you can even put your
Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff