Attic insulation - materials comparison

Paremon

Need to get an attic insulated on a retrofit (2 storey built in the 70s) & looking for some (impartial) advice from people in the know.

Current insulation: Loose fibreglass between joists, approx 75 to 100mm, which has flattened over time & is probably useless at this stage but will likely stay there.

Needs:
1. Attic insulation (warm or cold attic)
- Highest u-value rating possible without breaking the bank. Getting the right job done is the priority, if a cheaper option is available that does about the same thing then that will be chosen.
2. Attic flooring for storage (about 12sq m)
3. Additional ventilation
- I've been advised that the current ventilation isn't great with some of the soffit vents partly covered. Tile vents have been recommended.
4. Raise BER rating. Must be in low D or E class. I'm not getting a BER assessment before work is carried out, I already know its low. I'll get it done after all upgrade work is done the house.

Wants:
2. Longest insulation lifespan where possible
- I'd prefer not to have to be topping up rolled insulation in 5 years time
3. No compression of insulation under flooring
- Some installers have said there should be zero insulation material compression, others have said compressing about 1/4 of the insulation material shouldn't matter.

Insulation options:
These are the options that I've come across so far from installer quotes & from what I've seen in friends' & family's homes:

A. Warm attic:
1. Open cell spray foam between rafters, baffles with 50mm gap behind for airflow.

OR

B. Cold attic:
1. Rolled earthwool 300mm (on top of existing old ~100mm fibreglass).
From what I understand earthwool is a trademark & is sold as 'glass mineral wool' (which I assume could also be called fibreglass) or as 'rock mineral wool'. The terms earthwool, rockwool, mineral wool etc seem to be used interchangeably without clarifying the actual material.
2. EPS boards. e.g. kore-system.com/kore-products/roof-insulation/kore-loft/technical or similar
3. Kingspan boards (probably too expensive given the quantity)

Questions:
1. Warm vs cold attic: looking opinions on which to go for. I know that a cold attic will mean insulating anything above the joists insulation (pipes, tanks etc).
2. Insulation material: again looking for opinions on which to go for.
Getting a decent comparison & breakdown of the pros & cons of each of the above 3 options (4 or 5 options after considering earthwool is sold as different materials) is proving harder than I expected (vested interests, partial info etc).
Does anyone have a link to an independent & reliable resource that compares each of the above 3 options on a like for like basis, mainly as regards to U-value, price per sq meter, labour etc.

Some people (installers & home home owners not in the trade) seem to swear by spray foam on the rafters (warm attic) as it lasts longer, provides air tightness at the point of insulation, u-value etc. Others swing for rolled earthwool as its tried & tested, more cost effective etc. Budget is a consideration of course but the primary goal is to get the right job done well.

Any advice appreciated.

BryanF

That's a lot of questions..
(Needs) q1. Earthwool is cheapest, but thicker than foam or PI
2. Put mineral wool between joists, PIR over joists and attic board on top, screwed to joists, check strength of joists with eng/ carpenter
3. Ok
4. ok

Wants
1. Lifespan ? This is an attic, waste glass/plastic fibre insulation like earthwool is fine.
2. See 2 above
3. Don't walk on it and it won't compress

A. Warm attic - are you doing an attic conversion ? Or why would you heat the attic? Insulate at the floor unless you want all your heat going up to the rafters.

B.1. Get the earthwool it's cheap, it's not really itchy. Just clarify it is not 'rock wool' which is used in fire retardant applications and is more expensive that the likes of earthwool.
2. Eps not suitable for attic, other than to swap with PIR for under storage.
3. King span is a PIR - there are alternatives that may be a little cheaper, but 12m2 of PIR under storage area will cost you 100€ ?

Questions
1. Cold attic ('A' above)
2. Earthwool. This is a DIY job which will take a half a day. Don't over think this.

Paremon

Thanks.

Re;
"That's a lot of questions.."
- That's partly driven by differing & conflicting info from installers & online. The interchangeable terms used for the various types of 'wool' doesn't help any consumer that's not in the trade either. I chose one post with multiple questions, rather than multiple posts, assuming it was the better option to save time. Judging by the number of responses though it seems not. Lesson learned.

Re;
"2. Put mineral wool between joists, PIR over joists and attic board on top, screwed to joists, check strength of joists with eng/ carpenter.
B.1. Get the earthwool it's cheap, it's not really itchy. Just clarify it is not 'rock wool' which is used in fire retardant applications and is more expensive that the likes of earthwool."
- Thanks. To clarify, by 'mineral wool' you mean Earthwool (trademark) & specifically 'glass mineral wool' rather than 'rock mineral wool', correct?

Re;
"1. Lifespan ? This is an attic, waste glass/plastic fibre insulation like earthwool is fine."
- Yes, lifespan. I understand that Earthwool (either type) flattens & looses its effectiveness over time, is that not correct? If it is correct then after how many years approx should it be replaced or topped up? I'm conscious of the fact that as there will be flooring that too would need to be taken up.

Re;
"3. Don't walk on it and it won't compress"
- The question was in regards to the storage area flooring which is designed to be walked on, rather than the non-floored area, which I've no intention to walk on.
What are your thoughts on partially compressed insulation under storage flooring? E.g. avoid compression at all costs or it's no big deal if only 100mm of the 400mm insulation is compressed?

Re;
"A. Warm attic - are you doing an attic conversion ? Or why would you heat the attic? Insulate at the floor unless you want all your heat going up to the rafters."
- No attic conversion is being done, the attic will be used for storage only.
I'm wondering why some (customers & installers) swear by the more expensive spray foam on rafters as a better way to insulate an attic (even if its not converted) as opposed to insulating at floor level. By 'better' I mean more effective (warmer house).
If anyone else here has any thoughts on spray foam (warm attic) vs earthwool at floor level (cold attic) as regards recommendations that'd be great.

Re;
"B.1. Get the earthwool it's cheap, it's not really itchy. Just clarify it is not 'rock wool' which is used in fire retardant applications and is more expensive that the likes of earthwool.
2. Eps not suitable for attic, other than to swap with PIR for under storage.
3. King span is a PIR - there are alternatives that may be a little cheaper, but 12m2 of PIR under storage area will cost you 100€ ?"
- I've seen an attic which was insulated by an Electric Ireland contractor (for the EI grant) & EPS was used in the attic (same as used in EWI I believe) both under storage flooring & non-floored areas, hence the inclusion in my post.
Point taken that you don't think it should be used in an attic but how does EPS compare on a like for like basis with Earthwool price/performance-wise? In the UK it seems cheaper at least.

Re;
1. Cold attic ('A' above)
2. Earthwool. This is a DIY job which will take a half a day. Don't over think this."
- Thanks. No DIY in this case, using SEAI-approved installer. Don't worry, I'm not over thinking it, I'm just trying to separate fact from opinion to make sure an educated decision is made so that we don't get the 'wool' pulled over our eyes.

Thanks again for the response/advice.

BryanF

Any chance you'd tidy up your post above (use the quotation tags in future please) and just ask your questions 1,2,3 and so on.

Paremon

I tried that by clicking the quote icon & the multi-quote icon, no go with Chrome, it just opens a blank 'Reply to Thread' page, the same as the one I'm using for this reply.

There was also no option to italicize anything.

I don't think it's too difficult to read, all my responses start with a hyphen.

stcosmin

Hi experts
I plan to insulate my attic and I was wondering if there is an insulating material that can be used for this job that can also sustain weight. I was thinking to achieve 2 in 1 (insulation and storage area).
For now, I have the normal insulation loose fibreglass between joists.
Thank you

sydthebeat

stcosmin wrote: »

Hi experts
I plan to insulate my attic and I was wondering if there is an insulating material that can be used for this job that can also sustain weight. I was thinking to achieve 2 in 1 (insulation and storage area).
For now, I have the normal insulation loose fibreglass between joists.
Thank you

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