attic Insulation

tech · 27-10-2019 3:48pm #1

looking at getting more insulation into Attic,

what the best insulation to use, currnelty 8 inches above ceiling, is it worth using 4" insulation between the beams, just inside the tiles??

GolfNut33 · 27-10-2019 4:38pm

tech wrote: »

looking at getting more insulation into Attic,

what the best insulation to use, currnelty 8 inches above ceiling, is it worth using 4" insulation between the beams, just inside the tiles??

No. Best option is to bulk up on ground level. Roll across joists and lay the thickest you can afford.

listermint · 28-10-2019 12:39pm

tech wrote: »

looking at getting more insulation into Attic,

what the best insulation to use, currnelty 8 inches above ceiling, is it worth using 4" insulation between the beams, just inside the tiles??

No unless your going down the airtight route it's a waste of money.

If your going that route you'd want to make sure your roofing fabric is spot on and possibly get someone to spray the rafter gaps. They'd card between each beam for roof ventilation and spray to the card. Idea being to seal in the attic space from outside elements.

Ush1 · 29-10-2019 2:07pm

You'd only insulate at rafter level if your attic is converted or in use as a living space.

Make the insulation at the ceiling level as thick as you can.

listermint · 29-10-2019 3:28pm

Ush1 wrote: »

You'd only insulate at rafter level if your attic is converted or in use as a living space.

Make the insulation at the ceiling level as thick as you can.

tbh all rafters should be insulated. Its inside the buildings envelope. Living space or not. Its best of all worlds.

Calahonda52 · 29-10-2019 5:06pm

listermint wrote: »

..

If your going that route you'd want to make sure your roofing fabric is spot on and possibly get someone to spray the rafter gaps. They'd card between each beam for roof ventilation and spray to the card. Idea being to seal in the attic space from outside elements.

.
Are issues with open cell foam being used with impermeable cards, not airtight against the wall plate, leading to rotting rafters.
Best done by stripping off first meter of slates and fitting the cards properly and then backfill loose insulation along the ceiling joists, allowing about 50mm additional for wind loss on surface

listermint · 29-10-2019 5:57pm

Calahonda52 wrote: »

.
Are issues with open cell foam being used with impermeable cards, not airtight against the wall plate, leading to rotting rafters.
Best done by stripping off first meter of slates and fitting the cards properly and then backfill loose insulation along the ceiling joists, allowing about 50mm additional for wind loss on surface

Why wouldnt the cards be permeable ??

Calahonda52 · 29-10-2019 7:01pm

listermint wrote: »

Why wouldnt the cards be permeable ??

Any I have seen are black plastic or hard cardboard

Harry Palmr · 29-10-2019 8:04pm

Excuse me for jumping in with a query. Is it worth laying a foil barrier over existing attic floor insulation?
If so what type? Perforated/not perforated, bubble or smooth.

Calahonda52 · 30-10-2019 8:40am

Harry Palmr wrote: »

Excuse me for jumping in with a query. Is it worth laying a foil barrier over existing attic floor insulation?
If so what type? Perforated/not perforated, bubble or smooth.

No

D13exile · 30-10-2019 5:39pm

I laid Knauf between my joists and then another layer perpendicular to that to bring it to 400mms. After that, the return on adding more insulation over that drops off. Remember to leave your soffit vents free so air can circulate or you may end up with dampness on your roof timbers and long term issues down the road. Put a seal around your attic access hatch or consider replacing with a custom made hatch that is insulated and forms a tight seal when closed.

Calahonda52 · 30-10-2019 6:12pm

D13exile wrote: »

I laid Knauf between my joists and then another layer perpendicular to that to bring it to 400mms. After that, the return on adding more insulation over that drops off. Remember to leave your soffit vents free so air can circulate or you may end up with dampness on your roof timbers and long term issues down the road. Put a seal around your attic access hatch or consider replacing with a custom made hatch that is insulated and forms a tight seal when closed.

...
Best done by stripping off first meter of slates etc and fitting ventilation baffles that are airtight to the wall plate and sealed against the roof rafters so as the wind from the ventilated soffits cannot, repeat cannot, pass through the insulation.
.
insulation upgrade best done by backfilling loose insulation along the ceiling joists, allowing about 50mm additional for wind loss on surface.
.
The attached shows what happens when it is done as described above by exile and the wind passes through the insulation.
This was in a house with a hipped roof at this end so no chance of the roll me out from the attic hatch practice working: it made it worse.:eek:

D13exile · 30-10-2019 7:12pm

Calahonda52 wrote: »

...
Best done by stripping off first meter of slates etc and fitting ventilation baffles that are airtight to the wall plate and sealed against the roof rafters so as the wind from the ventilated soffits cannot, repeat cannot, pass through the insulation.
.
insulation upgrade best done by backfilling loose insulation along the ceiling joists, allowing about 50mm additional for wind loss on surface.
.
The attached shows what happens when it is done as described above by exile and the wind passes through the insulation.
This was in a house with a hipped roof at this end so no chance of the roll me out from the attic hatch practice working: it made it worse.:eek:

Method you describe would be impractical for the majority of DIY'ers and goes against standard practice, i.e. one layer between the joists and another perpendicular. I find the two knauf layers "knit" together eliminating any voids between the layers. Where there are soffit vents, I keep the insulation back from the vent leaving sufficient space for the air to enter and circulate over and above the insulation. I suppose if insulation was pushed close to the vents and a second layer idly thrown across the top, then yes it would leave a hole for air to run under and reduce/eliminate the effectiveness of the insulation and cause cold spots. I've insulated every house I've ever owned as I described above and never had any issue with mould in rooms as you show in that photo. I suspect there may be greater issues at play there including but not confined to insulation pulled too far back from the wall allowing cold spots in the ceiling.

However, I'm replacing the wooden soffit and fascia boards on teh 25 year old house I've bought next week and I will look into the fuller length vents as you describe in order to ensure no build up of moisture in my attic.

listermint · 30-10-2019 11:17pm

No need for full length vents. I put in vent every meter or so on mine. Replaced the timber rotten stuff with pvc last year. The vents do not run the full length.

D13exile · 31-10-2019 1:28pm

listermint wrote: »

No need for full length vents. I put in vent every meter or so on mine. Replaced the timber rotten stuff with pvc last year. The vents do not run the full length.

In the case of the house I bought, there was absolutely no maintenance done on it as far as I can tell from its poor condition since it was built. The timber fascia and soffits are rotten and will be replaced by fresh timber prior to the pvc cladding going on. I'm considering the longer vents as the roof timbers show signs of "sweating" in the past due to the existing soffit vents being blocked with insulation by the previous owner, the extractor van from the bathroom venting straight into the attic (and not piped outside) and up to 15 people living in the house when it was rented with the ensuing heavy amount of water vapour from that many people living in a three bed semi!!! I want to ensure that there is no moisture build up in the eaves of the roof space as I've heavily insulated the house now with insulated plasterboard on all interior walls and in the now converted attic space. While the house in now considerably warmer, all that warm moist air is going straight up to the attic and needs to get out somewhere. As I don't have the money for an expensive heat recovery systems, a simple cross airflow from soffit vents should (I hope) suffice in eliminating moisture build up in the eaves.

listermint · 31-10-2019 1:45pm

D13exile wrote: »

In the case of the house I bought, there was absolutely no maintenance done on it as far as I can tell from its poor condition since it was built. The timber fascia and soffits are rotten and will be replaced by fresh timber prior to the pvc cladding going on. I'm considering the longer vents as the roof timbers show signs of "sweating" in the past due to the existing soffit vents being blocked with insulation by the previous owner, the extractor van from the bathroom venting straight into the attic (and not piped outside) and up to 15 people living in the house when it was rented with the ensuing heavy amount of water vapour from that many people living in a three bed semi!!! I want to ensure that there is no moisture build up in the eaves of the roof space as I've heavily insulated the house now with insulated plasterboard on all interior walls and in the now converted attic space. While the house in now considerably warmer, all that warm moist air is going straight up to the attic and needs to get out somewhere. As I don't have the money for an expensive heat recovery systems, a simple cross airflow from soffit vents should (I hope) suffice in eliminating moisture build up in the eaves.

Does this not sound like new roof territory ? have you had that assessed fully ?

D13exile · 31-10-2019 3:44pm

listermint wrote: »

Does this not sound like new roof territory ? have you had that assessed fully ?

I had it fully assessed when I saw the evidence of moisture build up on the roof trusses. The roof timbers were individually assessed from apex right down to the wall plate and are still sound but given a few more years of moisture build up in the attic, I'd say rot would have set in. That's why I'm (perhaps) going overkill on the attic ventilation.

The external timbers that make up the soffit and fascia were never maintained and are beyond redemption which is why I'm replacing them prior to the pvc soffit and fascia going on.

listermint · 31-10-2019 5:10pm

D13exile wrote: »

I had it fully assessed when I saw the evidence of moisture build up on the roof trusses. The roof timbers were individually assessed from apex right down to the wall plate and are still sound but given a few more years of moisture build up in the attic, I'd say rot would have set in. That's why I'm (perhaps) going overkill on the attic ventilation.

The external timbers that make up the soffit and fascia were never maintained and are beyond redemption which is why I'm replacing them prior to the pvc soffit and fascia going on.

PVC Soffits and fasica is meant to be fixed to your rafters as that overhangs. There should be no replacement of any external timbers. unless of course you need droppers from the rafters to fix soffit or fascia to. But alot of installers use PVC offcuts as droppers so if you are getting a company to do it then dont bother replacing any timbers its not required.

if doing it yourself you can use either timber or pvc offcuts as droppers. You wont be fixing the PVC to an existing timber soffit.

D13exile · 01-11-2019 11:30am

listermint wrote: »

PVC Soffits and fasica is meant to be fixed to your rafters as that overhangs. There should be no replacement of any external timbers. unless of course you need droppers from the rafters to fix soffit or fascia to. But alot of installers use PVC offcuts as droppers so if you are getting a company to do it then dont bother replacing any timbers its not required.

if doing it yourself you can use either timber or pvc offcuts as droppers. You wont be fixing the PVC to an existing timber soffit.

Thanks for the advice but the existing timber fascia and soffits are literally falling to bits. A few chunks have come off at the edges where rain water runs down to. Birds have nested in the eaves where there was a hole here until I blocked it with some osb offcut until I could get a proper job done. Personally I wouldn't be happy covering what is effectively rotten wood in plastic keeping all that rot and moisture trapped under impermeable pvc. I'd be afraid the rot would spread up into the rafters in due course. Yes I'm probably overthinking this but I'd rather spend the extra now than have to perhaps rip off the new pvc fascia and soffit down the line.

As for doing it myself, I can tackle most jobs but not where heights are involved. I slipped on some algae/moss and fell off a roof once and luckily for me it was a bungalow and I landed in a soft flower bed. A few bruises but no broken bones.

listermint · 01-11-2019 2:07pm

D13exile wrote: »

Thanks for the advice but the existing timber fascia and soffits are literally falling to bits. A few chunks have come off at the edges where rain water runs down to. Birds have nested in the eaves where there was a hole here until I blocked it with some osb offcut until I could get a proper job done. Personally I wouldn't be happy covering what is effectively rotten wood in plastic keeping all that rot and moisture trapped under impermeable pvc. I'd be afraid the rot would spread up into the rafters in due course. Yes I'm probably overthinking this but I'd rather spend the extra now than have to perhaps rip off the new pvc fascia and soffit down the line.

As for doing it myself, I can tackle most jobs but not where heights are involved. I slipped on some algae/moss and fell off a roof once and luckily for me it was a bungalow and I landed in a soft flower bed. A few bruises but no broken bones.

Spend the extra now doing what?

Perhaps you have taken up what i said incorrectly.

When ripping out your existing fascias and soffits they will be binned. And when putting up the new PVC soffits and fascias. You will not be putting in timber before it. The PVC soffits and fascias are mounted to the rafters 'as is' they dont go on top of timber fascias or soffits. In some cases you will need droppers depending on lenght and depth or state of the rafters. These droppers can be timber or made from the PVC you are using.

I hope that makes sense.

It seems you think that you will be pullling out the timber sofit and fascia, putting in new timber sofit and fascia and then PVC over the top of that. which is not the way its done.

This video should explain visually what im talking about

https://www.youtube.com/watch?v=KtfvLCN883c

Muahahaha · 02-11-2019 10:57pm

Does anyone here have any feedback on Icenyne spray foam insulation? I've an unusual attic in that there is a bedroom inside it similar to a dormer bungalow so I think I have to go down the spray foam route. Also I got quoted 1,500 for 44sqm of spray foam, is this in the ball park or more expensive than others. Will be getting two more quotes anyway but am wondering if it is a typical price for the size of the job.

listermint · 03-11-2019 8:06am

Is the plasterboard all coming down to do this spray job?

If not then how are they doing it properly. Is there no insulation in the rafters already? Sounds quite unusual for a conversation to a bedroom

Muahahaha · 04-11-2019 1:08am

listermint it is not an attic conversion, the bedroom already exists with two different crawl spaces either sides of the walls. Within the crawl spaces there is no insulation between the rafters and limited insulation between the ceiling joists of the rooms below.

The company recommended spray foaming the 44sqm of space between the rafters inside these crawl spaces, said that this would create a warm space beneath the roof and thus the bedroom would be warmer. Also said no need to insulate the cold water tank doing it this way.

listermint · 04-11-2019 7:06am

Muahahaha wrote: »

listermint it is not an attic conversion, the bedroom already exists with two different crawl spaces either sides of the walls. Within the crawl spaces there is no insulation between the rafters and limited insulation between the ceiling joists of the rooms below.

The company recommended spray foaming the 44sqm of space between the rafters inside these crawl spaces, said that this would create a warm space beneath the roof and thus the bedroom would be warmer. Also said no need to insulate the cold water tank doing it this way.

How are they handling the ventilation of the timbers in these spaces.

Lumen · 04-11-2019 7:07am

I don't see how this job can be done properly (vent cards, AT, avoidance of voids) without taking down the plasterboard.

My limited experience of spray foam merchants is that their creativity of application is matched only by their complete denial of approved construction details.

GreeBo · 04-11-2019 5:53pm

tech wrote: »

looking at getting more insulation into Attic,

what the best insulation to use, currnelty 8 inches above ceiling, is it worth using 4" insulation between the beams, just inside the tiles??

Not sure whats to be gained if you already have 8" of insulation tbh...
Whats driving this idea? Do you have cold rooms etc?

Muahahaha · 04-11-2019 8:12pm

listermint wrote: »

How are they handling the ventilation of the timbers in these spaces.

He said that the spray foam is open cell and it 'breathes'

Lumen wrote: »

I don't see how this job can be done properly (vent cards, AT, avoidance of voids) without taking down the plasterboard.

My limited experience of spray foam merchants is that their creativity of application is matched only by their complete denial of approved construction details.

Thats my worry. He said that as part of the grant Ive to get a BER assessment done and that the assessor 'approves' the works. However Ive read enough posts on here to know that the BER assessment is not any indication of construction quality.

Anyway Ive uploaded three photos of the crawl spaces and the fourth photo is of a not to scale sketch of the attic with bedroom inside it.

https://ibb.co/RcmJ3jF
https://ibb.co/rfZq3SD
https://ibb.co/WVLb8hm
https://ibb.co/jHcSrQJ

I'm unsure what way to go. The company who quoted said its best to spray foam between the rafters, thus mitigating a cold roof and allowing the bedroom to be warmer overall. But from what Id gathered that doesnt include any insulation on the gable end or between me and my neighbour so Im thinking that it would still be cold. Is it better to just insulate the envelope of the bedroom and perhaps top up or replace the very old fibre insulation that is currently between the ceiling joists in the crawl spaces?

MicktheMan · 04-11-2019 11:27pm

Insulating between the rafters is a complete waste of time & money regardless of what you insulate with.
While your insulation levels could very well be improved, I suspect your major issue with the room in the roof is air leakage. Improving the insulation wont address this.

listermint · 05-11-2019 12:53pm

MicktheMan wrote: »

Insulating between the rafters is a complete waste of time & money regardless of what you insulate with.
While your insulation levels could very well be improved, I suspect your major issue with the room in the roof is air leakage. Improving the insulation wont address this.

This isn't true. Its a blanket statement.

Air tightness on its own doesn't work. You need a combination of insulation and airtightness. Whilst insuring the structure i.e rafters can breathe.

So blanket statement like insulation between rafters is a waste of money is not accurate.

MicktheMan · 05-11-2019 1:06pm

listermint wrote: »

So blanket statement like insulation between rafters is a waste of money is not accurate.

Based on the information provided, it is accurate.

MicktheMan · 05-11-2019 1:15pm

listermint wrote: »

Air tightness on its own doesn't work. You need a combination of insulation and airtightness.

I didn't say AT on its own. I advised to initially concentrate on the probable air tightness weaknesses rather than insulation weaknesses to address the largest heatloss component.

listermint · 05-11-2019 1:34pm

MicktheMan wrote: »

I didn't say AT on its own. I advised to initially concentrate on the probable air tightness weaknesses rather than insulation weaknesses to address the largest heatloss component.

If hes doing it he needs to look at it holistically. no point patching up airtight tape if the air behind the wall is same tempreture as the air outside the roof tiles.

Its not one or the other, its both.

MicktheMan · 05-11-2019 1:47pm

listermint wrote: »

If hes doing it he needs to look at it holistically. no point patching up airtight tape if the air behind the wall is same tempreture as the air outside the roof tiles.

Its not one or the other, its both.

Not necessarily. Depends where the thermal envelope is! Normally in room in roof situations, the thermal envelope follows up the knee walls making the crawl space behind the knee wall a cold space. By all means ensure the knee wall is insulated adequately, but this will have little impact unless and until the air tightness weaknesses are addressed.

Again, I never said its one or the other. I said to address the probable biggest issue first.

GreeBo · 05-11-2019 1:56pm

listermint wrote: »

If hes doing it he needs to look at it holistically. no point patching up airtight tape if the air behind the wall is same tempreture as the air outside the roof tiles.

There is though, reducing the number of times the air is exchanged in your house will have a massive impact on your heating.
Once the air stops changing/escaping its far easier to heat this air and maintain that heat in your house, even if that heat is still being lost to "cold walls".

Far slower to lose heat through an uninsulated wall than through an open window, for example.

listermint · 05-11-2019 2:41pm

GreeBo wrote: »

There is though, reducing the number of times the air is exchanged in your house will have a massive impact on your heating.
Once the air stops changing/escaping its far easier to heat this air and maintain that heat in your house, even if that heat is still being lost to "cold walls".

Far slower to lose heat through an uninsulated wall than through an open window, for example.

So we both agree both are necessary then....

yeah?

GreeBo · 05-11-2019 4:02pm

listermint wrote: »

So we both agree both are necessary then....

yeah?

Well depending on your goal you might need one much more than the other.

If I could only do one, or if I was to prioritize one it would be controlling air flow before adding more insulation.
You just cannot insulate away an air flow problem.

Muahahaha · 05-11-2019 5:07pm

Thanks for all the replies lads. Seems Im going to have to do a fair bit of research on this as whatever company I get out to quote will just try to sell me their solution regardless whether it will work or not. Had a dry lining company out earlier in the year and he suggested taking all the roof tiles off and insulating the roof proper at a cost of almost 6.5k :eek: So when the spray foam co. came out quoting 1.5k I thought it to be a lot more reasonable but its no use paying a cheaper price if it still isnt done right.

Im wondering is there any independent guidance documents out there from the likes of the NSAI or similar in regards to insulating an unusual attic such as this one or else what would be considered best practice? I know I definitely have an air tightness problem as the previous owner has shoved mounds of insulation near where the rafters meet the soffit/facia and I've seen other sections where there is daylight coming in here. Also a large birds nest in the attic tells me the same thing. Wondering is the junction between rafters and soffit supposed to be fully sealed and airtight? Or is there supposed to be a slim gap to allow airflow to ventilate the rafters and ceiling joists?

Lumen · 05-11-2019 5:13pm

It's not an unusual attic. There are probably hundreds of thousands of those in Ireland.

Not sure this is the latest.

https://www.engineersireland.ie/EngineersIreland/media/SiteMedia/groups/Divisions/civil/NSAI-Standard-Recommendation-S-R-No-105-of-2014-Code-of-Practice-for-the-Energy-Efficient-Retrofit-of-Dwellings.pdf?ext=.pdf

Muahahaha · 05-11-2019 6:31pm

Thanks Lumen, that document explains it clearly for me, specifically page 69 'Cold pitched roofs-insulation at rafters'.

One thing Im wondeirng though it does not mention anything about insulating the gable ends, both the exposed one (end of terrace) and the one adjoining my neighbour. I would have thought that it is important to have a continuous insulated envelope throughout the attic space? The gable ends are single block so no option for a cavity fill.

poker--addict · 16-01-2022 5:46pm

how big a difference will an extra layer of insulation make?

GreeBo · 19-01-2022 8:15pm

https://www.boards.ie/discussion/comment/118485294#Comment_118485294

It depends on whats already there.

Adding an 50mm to an existing 150mm probably wont do anything noticeable, adding 50mm where there is nothing will make a difference.

Adding 500mm badly will also do very little though.

attic Insulation

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