Garage Roof Insulation
- Thread starter Shadowfax
- Start date
Help Support UKworkshop.co.uk:
Shadowfax
Established Member
Hi Jake
I think you are right but I did press the point and was told that because of the single skin wall and the potential for heat loss there, as well as through the door, there would be nothing to worry about. Any minor interstitial condensation would simply run out of the bottom of the slope because of the foil backing. The guy felt (sorry!) that as roofing felt tends to "sweat" anyway there would be no real difference and it would not be worth worrying about it. All based on experience rather than tests and specifications, of course, and not covered by the Building Regs as they do not apply to garages.
Like I said, interesting. Still going to concentrate on the door, though.
Cheers.
SF
I think you are right but I did press the point and was told that because of the single skin wall and the potential for heat loss there, as well as through the door, there would be nothing to worry about. Any minor interstitial condensation would simply run out of the bottom of the slope because of the foil backing. The guy felt (sorry!) that as roofing felt tends to "sweat" anyway there would be no real difference and it would not be worth worrying about it. All based on experience rather than tests and specifications, of course, and not covered by the Building Regs as they do not apply to garages.
Like I said, interesting. Still going to concentrate on the door, though.
Cheers.
SF
I have been reading this thread with great interest, really surprizing what you can learn on the forum.
Can anyone enlighten me regarding an air gap btween insulation and roof where the roof is of the flat type?
I intend to do mine before next winter, floor ans walls are already done.
Can anyone enlighten me regarding an air gap btween insulation and roof where the roof is of the flat type?
I intend to do mine before next winter, floor ans walls are already done.
The exact same principles apply.
Vapour barrier on the hot side of the insulation to stop the warm damp air getting through to the cold side in the first place. Either a ventilated cavity or a vapour permeable membrane on the cold side to let any condensed vapour escape.
Just the same principle applies if you are insulating a loft - a dpm should go below the insulation to stop the warm damp house air condensing on the top of the insulation when it hits cold attic air, and dripping back down.
Loads of stuff on Celotex's website on types of flat roof, have a poke around.
Vapour barrier on the hot side of the insulation to stop the warm damp air getting through to the cold side in the first place. Either a ventilated cavity or a vapour permeable membrane on the cold side to let any condensed vapour escape.
Just the same principle applies if you are insulating a loft - a dpm should go below the insulation to stop the warm damp house air condensing on the top of the insulation when it hits cold attic air, and dripping back down.
Loads of stuff on Celotex's website on types of flat roof, have a poke around.
Shadowfax
Established Member
Just to continue the saga. I had to go back to Building Control again this afternoon so I asked the question again - this time of one of the Senior BCOs. No connection with the other guy from this morning. He was still out on site. I got the same answer though. But the assumption is that the space (workshop) is basically unheated except for a radiator which produces no moisture and not a high temperature such as would be found in the house.
He also suggested that it would be sensible to use semi-rigid batts made from mineral wool such as would normally be used to insulate a wall. They are made to be in contact with the outside skin of a wall and do not allow condensation to generate. His advice was aimed at allowing for a more balanced environment between winter and summer. In other words to control solar gain to an extent.
Like I said I am going to concentrate on the door but I am starting to enjoy this thread so keep your ideas and questions coming. We will be able to start our own advisory site soon!
Any the wiser, Waka?
Building the workshop from scratch is obviously the best move but it seems that changing things afterwards is a problem.
SF
He also suggested that it would be sensible to use semi-rigid batts made from mineral wool such as would normally be used to insulate a wall. They are made to be in contact with the outside skin of a wall and do not allow condensation to generate. His advice was aimed at allowing for a more balanced environment between winter and summer. In other words to control solar gain to an extent.
Like I said I am going to concentrate on the door but I am starting to enjoy this thread so keep your ideas and questions coming. We will be able to start our own advisory site soon!
Any the wiser, Waka?
Building the workshop from scratch is obviously the best move but it seems that changing things afterwards is a problem.
SF
If you don't heat it, there isn't a problem, same as if you have draughts everywhere. The atmosphere will be the same in and out, and on both sides of the insulation. And if you are going to heat it an hour or so here and there, that isn't going to make a huge amount of difference. That wasn't clear, all you said was that you were trying to save on heating costs! Use a dry heat source when you do heat it, and insulate how you like - but no point in using celotex in that case 'cos it would be way over the top for the requirements.
DaveL
Established Member
Well I have bought a roll of the metalised bubble wrap type stuff that I am going to fix on the bottom of the rafters. I have a staple gun for fixing it and some of the ali foil tape to seal the joints. It looked a good deal from ebay.
Of course I do need to move all of the timber that is stored in the roof space to be able to fix it up.
I also have lots of packs of laminate floor, along with DPM and insulating pads to go on the floor, its only the first line of the instructions I have a problem with:
Clear the room.
Just who are they kidding!
But I hope that once I have done this over the summer then next winter will be much more comfortable in the shop. Having a neighbour who brings me old pallets for fire wood will help as well.
Of course I do need to move all of the timber that is stored in the roof space to be able to fix it up.
I also have lots of packs of laminate floor, along with DPM and insulating pads to go on the floor, its only the first line of the instructions I have a problem with:
Clear the room.
Just who are they kidding!
But I hope that once I have done this over the summer then next winter will be much more comfortable in the shop. Having a neighbour who brings me old pallets for fire wood will help as well.
Thanks guys, I get the picture.
Shadowfax
Established Member
Sorry, Jake. I moved the goal posts didn't I? I knew what I meant but that was not what I wrote! I will heat the workshop, sometimes, but only enough to keep it from freezing the glue etc. That sort of thing.
One thing I would urge all of you who think expanded polystyrene is a cheap alternative to proper insulation - please think very carefully before you use it at all indoors. It is highly hazardous when it burns. It produces tremendous heat and thick, black noxious smoke that contains icocyanates and cyanide amongst other things. It also drips burning droplets so one fire quickly turns into several more and it burns very quickly. In short, it is horrible stuff! It kills in short order!
I won't have it in the house in anything but small quantities because I have seen what it can do.
More stories about this if you like!
Thanks to all who have contributed to this thread, especially Jake.
Best wishes .
SF
One thing I would urge all of you who think expanded polystyrene is a cheap alternative to proper insulation - please think very carefully before you use it at all indoors. It is highly hazardous when it burns. It produces tremendous heat and thick, black noxious smoke that contains icocyanates and cyanide amongst other things. It also drips burning droplets so one fire quickly turns into several more and it burns very quickly. In short, it is horrible stuff! It kills in short order!
I won't have it in the house in anything but small quantities because I have seen what it can do.
More stories about this if you like!
Thanks to all who have contributed to this thread, especially Jake.
Best wishes .
SF
No problem, my misconception really.
Building regs will allow poly as long as it is behind plasterboard to give half-hour fire resistance. Interested to know whether you think that is enough to deal with it?
What does poly-iso do in a proper fire then? I know it kind of goes brown and smoulders rather than doing the dripping balls of fire act to start with, but at full-blown house fire temperatures, does that still hold true?
Building regs will allow poly as long as it is behind plasterboard to give half-hour fire resistance. Interested to know whether you think that is enough to deal with it?
What does poly-iso do in a proper fire then? I know it kind of goes brown and smoulders rather than doing the dripping balls of fire act to start with, but at full-blown house fire temperatures, does that still hold true?
Shadowfax
Established Member
Hi Jake
The big trouble with polystyrene is that it burns very hot and the smoke and fumes from it are toxic. It melts and spreads while it burns and the heat it gives off is extreme. If there is an air gap around or above it the effect is even worse and the flame propogation is much quicker.
When polystyrene tiles were really popular, in the 70s and early 80s people used to ignore the fixing advice and use blobs of glue to install them on their ceilings. The air gap, though small, behind the tiles was enough to spread fire at an almost unbelievable rate. I have seen fire travel the line of a poly "picture rail" around a room faster than it could be followed!
The cyanide and stuff that it gives off make the smoke highly dangerous. It is said that one good breath of the stuff will knock you out and the second will kill you. This is why we have always been very wary of the product in all its forms.
As to the temperature in a fire situation - 600 degrees C at ceiling height could easily be increased to 1000 degrees C when this stuff is in the room. At those sorts of temperatures the chance of flashover, where everything in the room self-ignites, is high. The backdraught potential is even better - where the temperature is raised enough to mean that any inrush of air will lead to super expansion of the gases and create a smoke explosion. Once the cover for it is broken or burned away, melted or whatever, the fire can race away. Way past time to be getting out!
This is why I actually hate expanded polystyrene! It can be bad for your health in a major way.
It is a marvellous material but people do not understand its bad points. For me they mostly outweigh the good points.
Horrible stuff!!
Cheers.
SF
The big trouble with polystyrene is that it burns very hot and the smoke and fumes from it are toxic. It melts and spreads while it burns and the heat it gives off is extreme. If there is an air gap around or above it the effect is even worse and the flame propogation is much quicker.
When polystyrene tiles were really popular, in the 70s and early 80s people used to ignore the fixing advice and use blobs of glue to install them on their ceilings. The air gap, though small, behind the tiles was enough to spread fire at an almost unbelievable rate. I have seen fire travel the line of a poly "picture rail" around a room faster than it could be followed!
The cyanide and stuff that it gives off make the smoke highly dangerous. It is said that one good breath of the stuff will knock you out and the second will kill you. This is why we have always been very wary of the product in all its forms.
As to the temperature in a fire situation - 600 degrees C at ceiling height could easily be increased to 1000 degrees C when this stuff is in the room. At those sorts of temperatures the chance of flashover, where everything in the room self-ignites, is high. The backdraught potential is even better - where the temperature is raised enough to mean that any inrush of air will lead to super expansion of the gases and create a smoke explosion. Once the cover for it is broken or burned away, melted or whatever, the fire can race away. Way past time to be getting out!
This is why I actually hate expanded polystyrene! It can be bad for your health in a major way.
It is a marvellous material but people do not understand its bad points. For me they mostly outweigh the good points.
Horrible stuff!!
Cheers.
SF
Shadowfax":20u33q3y said:
Yes, notorious. I saw someone buying some the other day in a B&Q, thought they would have been banned.
Are the polyisocyanurates (eg celotex) any better in this respect though? I'm no chemist, but from the name they sound like they might give off cyanide too!
Celotex waffle on about how much better it is at fire resistance, but I've seen it burn, it just smoulders more rather than racing away. I suspect that at 600C, that might be a different story though - not that I have any reason to do so, which is why I'm interested.
Shadowfax
Established Member
Hi Jake
They are made from a different kind of foam. The chemical structure is different. Something to do with the polymer chains. Anything at all will burn if it gets hot enough but where man-made stuff is concerned we have tended to learn the hard way, I think.
The new foams burn differently, tending to seal up with the heat rather than freely releasing more material to burn even more. Even the look is different. Celotex is very dense whereas expanded foam is just loads of little balls joined together with a lot of air.
We will need a chemist to explain the theoretical differences but in practice my vote goes for the slower-to-react products. Anything that helps to prevent the building falling on top of me in a fire is all right with me!
Water+heat=steam=knock-down and cooling. Lovely!
SF
They are made from a different kind of foam. The chemical structure is different. Something to do with the polymer chains. Anything at all will burn if it gets hot enough but where man-made stuff is concerned we have tended to learn the hard way, I think.
The new foams burn differently, tending to seal up with the heat rather than freely releasing more material to burn even more. Even the look is different. Celotex is very dense whereas expanded foam is just loads of little balls joined together with a lot of air.
We will need a chemist to explain the theoretical differences but in practice my vote goes for the slower-to-react products. Anything that helps to prevent the building falling on top of me in a fire is all right with me!
Water+heat=steam=knock-down and cooling. Lovely!
SF
