Thoughts on insulation to be applied in attic conversion

[pbyrne]

Hi,

What would be the opinions of the masses when insulating an attic conversion - what type/thickness is best.

I have been doing some research and a neighbour of ours had a conversion done with the following:

200mm fibreglass to be fitted behind the walls of the new attic room

kingspan thermopitch 65mm rigid boards to be fitted between rafters on roof

internal ceiling will have gyproc foilback boards

In terms of average, good, very good - what rating would the above get - how could it be improved?

I am assuming it is in compliance with the building regulations as she obtained a cert of compliance after the conversion.

Thanks,

pbyrne

 

[sydthebeat]

Hi,

What would be the opinions of the masses when insulating an attic conversion - what type/thickness is best.

I have been doing some research and a neighbour of ours had a conversion done with the following:

200mm fibreglass to be fitted behind the walls of the new attic room

kingspan thermopitch 65mm rigid boards to be fitted between rafters on roof

internal ceiling will have gyproc foilback boards

In terms of average, good, very good - what rating would the above get - how could it be improved?

I am assuming it is in compliance with the building regulations as she obtained a cert of compliance after the conversion.

Thanks,

pbyrne

what do you mean

200mm fibreglass to be fitted behind the walls of the new attic room

do you mean in the 1.2 high stud walls?? If so then squashing 200mm into a 100mm space only equates to 100mm of insulation. generally the best solution here is 100mm PU board (xtratherm rafterlock) bewteen the rafters all the way from the eaves to the ceiling height, and across the ceiling in 150mm. then slab out with 47.5 insulation backed platerboard... 35mm insulation and 12.5 plasterboard. I wouldnt insulate in the small stud walls... because people use the air cavity as storage space and incorporate doors into these walls.

 

[pbyrne]

what do you mean do you mean in the 1.2 high stud walls?? If so then squashing 200mm into a 100mm space only equates to 100mm of insulation. generally the best solution here is 100mm PU board (xtratherm rafterlock) bewteen the rafters all the way from the eaves to the ceiling height, and across the ceiling in 150mm. then slab out with 47.5 insulation backed platerboard... 35mm insulation and 12.5 plasterboard. I wouldnt insulate in the small stud walls... because people use the air cavity as storage space and incorporate doors into these walls.

hi syd (I was hoping you would read this, always good info from you),

what do you mean do you mean in the 1.2 high stud walls??

Yes - I think that is what she meant, the little internal stud wall around the room would have insulation on the back of it. When you say 100mm - do you mean that is the typical thickness of the studs/battons that are behind that wall? Perhaps the intention was that the extra 100mm would extrude into the cavity space (vertically).

A picture on p7 of the following probably shows what she means:
[broken link removed]

I wouldnt insulate in the small stud walls... because people use the air cavity as storage space and incorporate doors into these walls.

Yes - that is the case here also - it is used as storage space with doors. Would you say then that insulating the stud walls is redundant if the rafters are insulated all the way down to the eves (unlike the SEI diagram above?)

 

[sydthebeat]

Yes - that is the case here also - it is used as storage space with doors. Would you say then that insulating the stud walls is redundant if the rafters are insulated all the way down to the eves (unlike the SEI diagram above?)

If you check the next page (page 8.) see the top pic showing the pitched roof with attic space, this is what i mean. I would recommend it even more if you plan on using the cavity as storage space. It may be slightly more awkward work, but it is definitely with it compared with the alternative.

 

[pbyrne]

If you check the next page (page 8.) see the top pic showing the pitched roof with attic space, this is what i mean. I would recommend it even more if you plan on using the cavity as storage space. It may be slightly more awkward work, but it is definitely with it compared with the alternative.

Thanks for that syd - the plan would be to make use of the room as an "attic room" as they have it on those diagrams. What would be the benefit do you think of doing it your way (picture1 on p8) versus insulating the stud wall (pciture2 on p8)?

 

[sydthebeat]

If you use the cavity space as storage then you need access to it. therefore your insulation envelope is compromised at every access point... and in those situations the compromise is significant. You cant insulate behind the door access.

Doing it 'my way' you will end up with a complete uncompromised insulation envelope and a fully accessible storage area.

 

[pbyrne]

aha - that makes sense - thanks syd

 

[pbyrne]

Hi All,

Back looking at this now - have decided to go ahead with the job so finalising our specification.

Would people generally remove the current insulation that is above the ceilings in the bedrooms - so it is the insulation where the floor will be. I have been reading around a bit and opinion seems divided. The insulation we have in there at the moment is ancient and probably pretty rubbish so it would be no harm to either remove it completely or replace it.

I can see the logic in replacing it and I can also see the logic in removing it. Any thoughts to sway me either way?

For my conversation with the attic conversion people - what would be the advantage of "xtratherm rafterlock" over the "kingspan thermopitch 65mm rigid boards" they are recommending?

Thanks,

pbyrne.

 

[davidoco]

For my conversation with the attic conversion people - what would be the advantage of "xtratherm rafterlock" over the "kingspan thermopitch 65mm rigid boards" they are recommending?

65mm of thermapitch is not really up to the job although it probably does meet the building regulations for refurbishment. See here [broken link removed] for tables. Be carefuly when reading the tables and note at the bottom of each one that the underside of your rafter must be lined with 25 mm insulation backed plasterboard to meet the stated u value.

Rafterloc comes in at minimum size of 100mm.

 

[sydthebeat]

plus rafterloc is custom-made for this purpose, youd have to ensure the rigid boards is cut exceptionally well...

 

[pbyrne]

Thanks for those replies - in terms of cost is there a massive difference between the two products?

I have no idea how much I would require but say it was 100sq. meters - what would be the price approximately for each one.

Thanks again.

 

[pbyrne]

65mm of thermapitch is not really up to the job although it probably does meet the building regulations for refurbishment. See here [broken link removed] for tables. Be carefuly when reading the tables and note at the bottom of each one that the underside of your rafter must be lined with 25 mm insulation backed plasterboard to meet the stated u value.

Rafterloc comes in at minimum size of 100mm.

Hi,

Had a chat with a company that is contracted by SEI to provide insulation advice and through the conversation we worked out:

(1) The rafters on the roof are 4inches thick - so I think that limits greatly the thickness of the thermopitch we can put in. Looks like 65mm is the max to allow enough breathing space for air to circulate. Is that correct or could we go up to 75mm - they were not exactly sure if that was ok.

(2) If the minimum thickness of the rafterloc is 100mm then I cannot use that so need to look at the kingspan (or equivalent). If going with the kingspan I need to be aware of the point made above by davidoco in relation to the requirement for insulated plasterboard on the underside of each rafter also.

(3) As discussed above - insulated plasterboard is the right man for the stud walls. The 47.5mm stuff mentioned by syd above looks like it will do nicely - need to just research a specific product.

(4) We are not going to insulate the interior floor of the attic - so that heat can rise from the bedrooms up to the attic room. We may however soundproof it a bit while the floor is up.

(5) I am going to insulate all the way from the top of the roof to the eves with the thermoboard as suggested by syd above.

(6) I will also be insulating the floor of the storage area - undecided on that though - anybody have a comment on that - I think it is required. If insulating it some of the 65mm kingspan thermopitch would do fine (but might be an expensive way of doing it when compared to just putting 200mm of fibreglass down - comments?)

Almost there - hope this turns into a useful reference for other people considering an attic conversion!

Anybody care to comment on whether I am correct on the above points or am I still missing a trick. Thanks.

 

[davidoco]

Thanks for those replies - in terms of cost is there a massive difference between the two products?

I have no idea how much I would require but say it was 100sq. meters - what would be the price approximately for each one.

Thanks again.

Rafterloc 100mm around €15 sq m. I've have not idea how much TP costs.

 

[davidoco]

Looks like 65mm is the max to allow enough breathing space for air to circulate. Is that correct or could we go up to 75mm - they were not exactly sure if that was ok.

mmm they were not sure and they are advising the SEI!

50mm if you have felt non breathable, 25mm if you have breather membrane.

Have a think about sheeps wool which you can (they claim) stuff in full fill, in your case 100mm, which comes in at about €13 per sq m for 100mm.

(6) I will also be insulating the floor of the storage area - undecided on that though - anybody have a comment on that - I think it is required. If insulating it some of the 65mm kingspan thermopitch would do fine (but might be an expensive way of doing it when compared to just putting 200mm of fibreglass down - comments?)[/quote

I don't think it's a good idea to put down thermopitch between your downstairs and insulated storage space - it defeats the purpose of insulating from eves plus it will cause a build up of moisture under the boards as you very likely don't have a vapour membrane on your ceiling or a minimum of foil backed plasterboard.

 

[sydthebeat]

thermapitch is fine as long as you cut it correctly... even thermafloor, which is basically the same product and may be cheaper than thermawall...

65mm between rafters and then slab out with 47.5 thermawall product will be a good construction.

You wouldnt have to insulate the floor of the storage space or within the stud walls, seeing as your insulating from eaves to ridge.... to be honest it would be overkill... you be better off offsetting the costs onto something else....

you can protect against noise by adding a cork or rubber mat product over the joists before laying the floor, as most airboure noise is transmitted through solids and not air...

just remember to leave sufficient airgaps at eaves and ridge to allow for ventilation to exhaust potential condensation water vapour.....

 

[pbyrne]

Hi,

Final question hopefully - waiting to hear back from sheep wool people for further information but wanted to see if anybody knows how the two finalists listed above would compare.

In the red corner we have:

75mm thermapitch (TP10) from kingspan + kooktherm k18 insulating dry-lining board (37.5mm),
uvalue = around 0.27 (that look correct)
thermal resistance = 3.25 m2.KW
cost = <need to find> per sq. m

In the green corner we have:
www.sheepwoolinsulation.ie
Premium Insulation Roll 400mm(W)x100mm(T)x4m(L) - 3 Roll Pack

uvalue = <need to find>
thermal resistance = looks to be specified in a different form:
[broken link removed] - how can I compare?
cost = roughly 15euro per sq. meter (or 10.5 per sq. meter for comfort range)

Can anybody help me map the specifications from one to the other so I can compare easily.

It would certainly look like the sheep wool is much easier to fit but I am getting the feeling that it does not perform as well as the thermapitch.

Thanks again for all the help on this.

 

[davidoco]

Premium Insulation Roll 400mm(W)x100mm(T)x4m(L) - 3 Roll Pack

uvalue = <need to find>
thermal resistance = looks to be specified in a different form:
[broken link removed] - how can I compare?
cost = roughly 15euro per sq. meter (or 10.5 per sq. meter for comfort range)

You would need to add the 50mm K8 insulating dry-lining board under the 100 mm wool. You should email sheepswool and enquire about that. They want you to put 140 wool under joints to get 0.15

 

[Franm]

Hi PByrne,
I can't help you map the specifications but it's my understanding that the insulation performance of sheeps wool is similiar to that of rockwool, fibreglass and hemp and that basically you need almost twice as much of it to get to the same value as the Kingspans/Xtratherms Phenolic products. i.e. 75mm of Phenolic = 150mm of sheeps wool. Having said that, there are other advantages to the wool such as fitting, breathability, ECO friendly etc. I also must hasten to point out that I'm no technical expert on this, I'm just a diy researcher who's trying to come up with a good solution for our own renovation project.

Re my project. I'm currently wondering if it might be possible to staple a breather membrane to the felt side (top) of the rafters and down 50mm thereby maintaining the required ventilation gap. Fit the Kingspan (or equivalent) product perpendicular to the rafters and pump fill the newly created cavity with say cellulose. This should overcome the issue/risk of poor fitted solid insulation and also allow the timber to breathe. This is just a (an amateurs) thought I had recently as I struggle to overcome my insulation challenges. Which are of course great mind occupiers as you probably already know.

Good luck & keep posting your findings/thoughts. I for one appreciate them.

Fran
ps Other readers, please correct me if I've anything wrong in the above

 

[sydthebeat]

Fran,

Your aim is to be applauded .... however id make the following points.

1. either allow the whole construction to breathe, or dont.
2. the kingspan insulation will restrict the breathability of the construction
3. the felt, assuming its non-breathable will also restrict the breathability

so either
1. build with non breathable felt, kingspan between the rafters and maintainyour 50mm gap.. if you want more performance then slab out with insulation backed plasterboard, and skim..

or

2. build in breathable construction.... use breathable felt, maintain the 50mm airgap (required by regs!) by either counterbattening above the rafters, or incorporating it in the rafter depth, use breathable insulation, sheepwool, hemp, softboard, rockwool etc... use a breather membrane and panel vent boarding....

 

[pbyrne]

Hi Folks,

Just a quick update on the thinking so far -

I am going to rule out the sheepwool as an option, if the 100m was the only thing required between the rafters then i would have kept it on the list but given that i will need an additional board i am going to stick to that approach - given that is what our conversion company are most likely to be comfortable with.

So now we are down to one approach - thermapitch + insulating board. I rang the kingspan technical services people yesterday, very impressed with how helpful they were - not as good as AAM experts but not bad!

An interesting point came up (again) about the layout of the insulation - they recommend not going from ridge of roof to eves - they recommend going from the ridge of the roof to the top of the stud wall, then insulating the back of the stud wall (as per SEI diagram above).

Now I completely forgot to ask them about syd's point above in relation to insulating the storage area because you will have a door that is kinda defeating the insulation - must give them a call back on that. Their logic in recommending that approach was that you are wasting heat going up from the bedrooms to the storage area and you should trap it there will insulation on the floor of the storage area.

After running through my scenario I ended up with two options from them:

(A) 50mm of the TP10 thermaboard + 82.5mm of K18 kooltherm insulated dry-lining. This costs approximately 32euro per sq. meter (8.70 + 22.90)

(B) 50mm of K7 (which is higher performance) + 72.5mm of the K18 insulated dry-lining board. This costs approximately 32.90euro per sq. meter (13.10 + 19.80)

Not much in the difference really and both would give me a u-value of about 0.2 which is probably as good as I can get in my situation.

Then for the stud wall we could continue to go with 82.5mm or 72.5mm insulated dry-lining and that would do it.

So I think that is it - be interested to hear any final points on the approach : ridge to eves VS ridge to stud + stud but apart from that I think we can say - done!

Thanks very much again to all contributors - has helped me alot.