Garage ceiling insulation
Discussion
We have a pretty typical 1930s style house, garage built into the house with a room above it. The trouble is there is naff all insulation in the ceiling of the garage or underfloor in the room above and it gets really cold in there, so I'm looking at sorting it out before it gets too cold.
The ceiling currently has plasterboard on it but the fixings have failed in a couple of places so it's falling down, so rather than attack from above I want to do this from below. What's the best way of doing this? What insulation should I be using?
I'm assuming something like Cellotex with new plasterboard sheets below it? I also want to use fireboard (is that the right wording?) as it's my sons bedroom that's above it, are there anything I should know about it before attempting this?
The ceiling currently has plasterboard on it but the fixings have failed in a couple of places so it's falling down, so rather than attack from above I want to do this from below. What's the best way of doing this? What insulation should I be using?
I'm assuming something like Cellotex with new plasterboard sheets below it? I also want to use fireboard (is that the right wording?) as it's my sons bedroom that's above it, are there anything I should know about it before attempting this?
Assuming you've got 200mm deep floor joists then I'd fit 100mm rigid PIR insulation (Celotex, Kingspan etc...) flush with the bottom of the joists. Ali foil tape over all the joints (board to board - joist to board) I'd stuff mineral wool insulation up the small gap between the first joist and the wall. Next I'd board over the whole ceiling with 25mm PIR insulation. Tape the joints again.
Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
mk1fan - thanks very much for the detailed description!
One issue I have thought of which it's made me consider is that the fuse board is in the garage and all the cables go up into the ceiling and route from there. Presumably if I board as close as I can to the cables and then use the sealant that would help with sealing them off?
One issue I have thought of which it's made me consider is that the fuse board is in the garage and all the cables go up into the ceiling and route from there. Presumably if I board as close as I can to the cables and then use the sealant that would help with sealing them off?
mk1fan said:
Assuming you've got 200mm deep floor joists then I'd fit 100mm rigid PIR insulation (Celotex, Kingspan etc...) flush with the bottom of the joists. Ali foil tape over all the joints (board to board - joist to board) I'd stuff mineral wool insulation up the small gap between the first joist and the wall. Next I'd board over the whole ceiling with 25mm PIR insulation. Tape the joints again.
Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
Do exactly this!Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
We have done this, apart from 2 layers of plasterboard.
mk1fan said:
Assuming you've got 200mm deep floor joists then I'd fit 100mm rigid PIR insulation (Celotex, Kingspan etc...) flush with the bottom of the joists. Ali foil tape over all the joints (board to board - joist to board) I'd stuff mineral wool insulation up the small gap between the first joist and the wall. Next I'd board over the whole ceiling with 25mm PIR insulation. Tape the joints again.
Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
I did this in my son's flat which is a top floor in a 30s block. There's a concrete slab roof topped with asphalt. Celotex with aluminium foil tape to seal the warm/moist room from the cold concrete ceiling and finished with a suspended false ceiling. In the case of a garage, though, the warm side is above and you have to stop warm moist air from leaking downwards past the Celotex so taping the upper side of the joints would seem to make more sense, surely? I am buying a house with integral garage and the floors of the upper storey are concrete. I want to insulate these from below. I am hoping that the concrete floor/garage ceiling is already a vapour barrier against room moist air causing interstitial condensation.Then fix two layers of 12.5mm plasterboard. Stagger the joints. At the very least point all the joints and edges with an intumescent sealant. Surface fix electric fittings or cables (or any other service) below the ceiling.
The above may be more expensive and there are certainly cheaper ways of doing it. However, the above 'warm' construction will not cause any issues with interstitial condensation, maintain a service void for power etc.. under the floor boards and provide sufficient fire compartmentation of the garage. It will also pauy back very quickly.
motco said:
you have to stop warm moist air from leaking downwards past the Celotex so taping the upper side of the joints would seem to make more sense, surely?
If access is available from the top then I would include taping the bedroom side joints as well as the garage side. However, as long as one side is [properly] taped and the boards a tightly fitted then it will, in practical terms, be sufficient.If access becomes available at a later date then I would tape the joints then and add (as suggested above) a layer of 100mm mineral wool for accoustic insulation.
Hi MK41,
Not wanting to drag up an old thread but you provided some useful advice to the original poster so I would like to ask some additional questions if that is ok.
The questions are not 'questioning' your advice, simply me trying to understand why you have given such info. I want to insulate the garage ceiling as best as possible and cost is not overly critical (within reason!!)
I to am just about to re-insulate my garage ceiling as per the original poster, and currently have full access underneath. Joists are 200mm deep and spacing between joists is ~ 370mm. I do not yet have access from above but may in future when relaying carpets etc.
I was going to install as you recommend with the 100mm PIR between the joists (fitted as tightly as possible) then put a layer of 12mm plasterboard direct onto the joists.
Questions:
1) I want to use a rigid PIR board and was looking initially at the Celotex GA4000. Is this sufficient? If not what would you suggest. There is a myriad of options out there so difficult to determine which is best.
2) You say take with aluminium foil tape joist to joist and joist to PIR board. I will have no board to board joints so I assume in my instance taping from the underside and bridging from one insulation board, across the underside of the joist to the next insulation board is ok. Also insulation board to wall?
3) Why do you suggest installing 25mm PIR board fixed to the underside of the joists and directly under the 100mm PIR board thats between the joists? What additional purpose does this give?
4) Why do you suggest 2 layers of 12mm plasterboard? Benefit over just 1 layer?
5) Given the rigid PIR board, is there any benefit to the fibreglass insulation inserted above the 100mm PIR in the void between upper side of PIR and underside of floorboard? What is this?
It was suggested to me previously that I am better of not placing the ridid PIR board between the joists, but actually placing it on the underside of the joist. The reason given was a reduced heat loss through the floor that would be created by all the joints if the PIR is fitted between the joists. Is this plausible or is the additional heat loss (if any) so negligible that it makes no difference? I would prefer not to do this as it significantly reduces the ceiling height if done so.
Many thanks and look forward to your response.
Not wanting to drag up an old thread but you provided some useful advice to the original poster so I would like to ask some additional questions if that is ok.
The questions are not 'questioning' your advice, simply me trying to understand why you have given such info. I want to insulate the garage ceiling as best as possible and cost is not overly critical (within reason!!)
I to am just about to re-insulate my garage ceiling as per the original poster, and currently have full access underneath. Joists are 200mm deep and spacing between joists is ~ 370mm. I do not yet have access from above but may in future when relaying carpets etc.
I was going to install as you recommend with the 100mm PIR between the joists (fitted as tightly as possible) then put a layer of 12mm plasterboard direct onto the joists.
Questions:
1) I want to use a rigid PIR board and was looking initially at the Celotex GA4000. Is this sufficient? If not what would you suggest. There is a myriad of options out there so difficult to determine which is best.
2) You say take with aluminium foil tape joist to joist and joist to PIR board. I will have no board to board joints so I assume in my instance taping from the underside and bridging from one insulation board, across the underside of the joist to the next insulation board is ok. Also insulation board to wall?
3) Why do you suggest installing 25mm PIR board fixed to the underside of the joists and directly under the 100mm PIR board thats between the joists? What additional purpose does this give?
4) Why do you suggest 2 layers of 12mm plasterboard? Benefit over just 1 layer?
5) Given the rigid PIR board, is there any benefit to the fibreglass insulation inserted above the 100mm PIR in the void between upper side of PIR and underside of floorboard? What is this?
It was suggested to me previously that I am better of not placing the ridid PIR board between the joists, but actually placing it on the underside of the joist. The reason given was a reduced heat loss through the floor that would be created by all the joints if the PIR is fitted between the joists. Is this plausible or is the additional heat loss (if any) so negligible that it makes no difference? I would prefer not to do this as it significantly reduces the ceiling height if done so.
Many thanks and look forward to your response.
Holy thread ressurection Batman!
No drama's.
1. Celotex GA4000 is their standard / basic board. It is directly comparable to the 'off the shelf' boards available from other manufacturers such as Ecotherm. Other boards are available that perform better (give the same insulation for thinner boards) but these are expensive and may well be a special order. I'd happily use Ecotherm, Kingspan or Celotex as I size from standard performance boards rather than high performance ones.
2. You can get ali foil tape in 100mm wide rolls so if your only joints are with the joists and the perimeter edges then yes, tape straight over. You may have one joist that is set 25-50mm off the wall. I would fill / pack this gap with mineral wool insulation (and tape over the underside) as it's easier than trying to get the PIR in. That said, if you've got the time then feel free to use PIR.
3. The 25mm PIR is a thermal break. As you later say, the joists bridge the PIR fitted between them so will be a path for heat transfer. The 25mm breaks this. You could just fit 100mm below the joists but, as you go on to say, this would reduce headheight.
4. Purely for fire compartmentation. A garage is a high risk area for fire (and fumes) so a good barrier is worthwhile. 2 layers of standard 12.5mm plasterboard should provide 60-minutes fire protection. Secondly, having two layers with staggared joist removes direct paths for fire and fumes through the joints. You could use 2 layers of 12.5mm Fireboard instaead for additional security.
5. The mineral wool insulation is purely for accoustic insulation. Sound is a funny thing and by fitting the PIR insulation you're creating a sealled box which could amplify / transmit sound very effectively.
HTH.
No drama's.
1. Celotex GA4000 is their standard / basic board. It is directly comparable to the 'off the shelf' boards available from other manufacturers such as Ecotherm. Other boards are available that perform better (give the same insulation for thinner boards) but these are expensive and may well be a special order. I'd happily use Ecotherm, Kingspan or Celotex as I size from standard performance boards rather than high performance ones.
2. You can get ali foil tape in 100mm wide rolls so if your only joints are with the joists and the perimeter edges then yes, tape straight over. You may have one joist that is set 25-50mm off the wall. I would fill / pack this gap with mineral wool insulation (and tape over the underside) as it's easier than trying to get the PIR in. That said, if you've got the time then feel free to use PIR.
3. The 25mm PIR is a thermal break. As you later say, the joists bridge the PIR fitted between them so will be a path for heat transfer. The 25mm breaks this. You could just fit 100mm below the joists but, as you go on to say, this would reduce headheight.
4. Purely for fire compartmentation. A garage is a high risk area for fire (and fumes) so a good barrier is worthwhile. 2 layers of standard 12.5mm plasterboard should provide 60-minutes fire protection. Secondly, having two layers with staggared joist removes direct paths for fire and fumes through the joints. You could use 2 layers of 12.5mm Fireboard instaead for additional security.
5. The mineral wool insulation is purely for accoustic insulation. Sound is a funny thing and by fitting the PIR insulation you're creating a sealled box which could amplify / transmit sound very effectively.
HTH.
Jeez mk1fan, you're some sort of insulation pervert! I'm definitely going to check back when I do any insulation jobs in future!
I'm reading the Haynes book on insulation at the moment (http://www.amazon.co.uk/Home-Insulation-Manual-comfortable-Manuals/dp/0857332759/ref=sr_1_1?s=books&ie=UTF8&qid=1409662035&sr=1-1&keywords=haynes+insulation) - I must look like a right spod on the way to work on the train
. Nice to see that what it seems to say is what the practice is in reality.
Might be worth knowing (and mk1fan, your opinion worth having), that there's a site where you can by Kingspan's seconds here: http://www.secondsandco.co.uk/. I've used them previously.
I'm reading the Haynes book on insulation at the moment (http://www.amazon.co.uk/Home-Insulation-Manual-comfortable-Manuals/dp/0857332759/ref=sr_1_1?s=books&ie=UTF8&qid=1409662035&sr=1-1&keywords=haynes+insulation) - I must look like a right spod on the way to work on the train
. Nice to see that what it seems to say is what the practice is in reality. Might be worth knowing (and mk1fan, your opinion worth having), that there's a site where you can by Kingspan's seconds here: http://www.secondsandco.co.uk/. I've used them previously.
Thanks for the quick reply MK41!
The garage is no longer used as a garage per se, a car will never fit in there. At least not in my tenure!
I appreciate double plasterboard is required to meet building regs but is a single layer of fireboard not sufficient?
Regarding the additional 25mm PIR, the upper of this and the underside of the 100mm will be in contact. Correct?
Regarding the fibreglass insulation, do you suggest this fills the void (100mm deep) or just partially fills? Any suggestions on type of insulation or just cheapest available at the time.
EggsB - What was the quality of the seconds Kingspan? Sufficient I assume if you are recommending. I have come across another site but from the images they uploaded of each batch they looked quite damaged.
The garage is no longer used as a garage per se, a car will never fit in there. At least not in my tenure!
I appreciate double plasterboard is required to meet building regs but is a single layer of fireboard not sufficient?
Regarding the additional 25mm PIR, the upper of this and the underside of the 100mm will be in contact. Correct?
Regarding the fibreglass insulation, do you suggest this fills the void (100mm deep) or just partially fills? Any suggestions on type of insulation or just cheapest available at the time.
EggsB - What was the quality of the seconds Kingspan? Sufficient I assume if you are recommending. I have come across another site but from the images they uploaded of each batch they looked quite damaged.
AdamW said:
EggsB - What was the quality of the seconds Kingspan? Sufficient I assume if you are recommending. I have come across another site but from the images they uploaded of each batch they looked quite damaged.
It varied is what I'd say. Some boards you wouldn't know - bit tatty round the edges, or bits of foil missing, (easily remedied if you're already using the ali tape). On some boards the interior foam hadn't worked out well, so you got bits that were floppy because there was a void in the board where there was no foam. It's easy to see these bits, and as I was using the 'cut bits to go in between joists/rafters' method, most of the boards got cut up anyway - I didn't find it the case that I found boards that were a complete write off. Those were the 'worst' ones - there were a few that sort of folded in the middle because the foam just wasn't there across the whole width for a sort of diagonal strip a couple of cm wide. Again, my heart sank, but in the end I just put them to one side, and found that when I needed odds and ends, I cut them up. I ended up with a pile of insulation boards well over 6' tall for about 130 quid 10 years ago. Worth a look, I'd say. They're a friendly lot as I recall too.When you're cutting them, use a saw guide, or a big table saw if you have one. Or make a saw guide and use a circular saw (makes lots of mess!). I did a few where I didn't, and ended up with wonky lines that wouldn't fit the gaps, so had to use expanding foam to fill the gaps. That stuff costs, but if you leave the gap, you're wasting your time. Best to cut straight and carefully.
I just cut mine with a hand saw and foamed the gaps with a foam gun (http://www.screwfix.com/p/no-nonsense-foam-applicator-gun/28483). The gun is less than £20 and the cans are less than £4 each. I used less than one can for a large single garage.
The gun allows you to control the flow of foam so you can get it into really small gaps. Make sure you get a can of foam remover as well!
The gun allows you to control the flow of foam so you can get it into really small gaps. Make sure you get a can of foam remover as well!
Spudler said:
AdamW said:
I appreciate double plasterboard is required to meet building regs but is a single layer of fireboard not sufficient?
Most inspectors will want to see two layers (must be staggered) of fire board now.If one board then must be skimmed.
See page 15:
http://www.british-gypsum.com/~/media/Files/Britis...
Evening.
To clarify, my advice is for DIY improvement not a notifiable job under the Building Regs. That's not to say it would be unsafe / wrong just that it's slightly alternative.
As stated already, if you want to use only one layer of plasterboard then I'd get it skimmed to get it 'sealed up' properly. ie close up all the gaps.
I would whole heartedly recommend getting a Celotex Board Saw as they noticeably reduce the amount of dust produced. A fine tooth tennon saw does the same but the Celotex saw is only £10 ish from Toolstation.
Using expanding foam is fine just check your choosen product doesn't melt the PIR board.
As for mineral wool, I just used 100mm loft roll. Readily available.
Thanks for the compliments but I'm way short of being a real insulation geek.
To clarify, my advice is for DIY improvement not a notifiable job under the Building Regs. That's not to say it would be unsafe / wrong just that it's slightly alternative.
As stated already, if you want to use only one layer of plasterboard then I'd get it skimmed to get it 'sealed up' properly. ie close up all the gaps.
I would whole heartedly recommend getting a Celotex Board Saw as they noticeably reduce the amount of dust produced. A fine tooth tennon saw does the same but the Celotex saw is only £10 ish from Toolstation.
Using expanding foam is fine just check your choosen product doesn't melt the PIR board.
As for mineral wool, I just used 100mm loft roll. Readily available.
Thanks for the compliments but I'm way short of being a real insulation geek.
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