Foam roof Insulation; Anyone had it done??

Hello all,

I'm currently building an ICF Dormer style house. All walls are complete and roof has just been felted.

My original plan to achieve good air tightness and insulation levels (as going to install a HRV system) was to put Insulation panels on the roof and THEN felt over them but that plan went out the window when my engineer said I'd have to drill through the panels and install the slate type roof ventilators to allow the roof to breath.

Anyway, from my preliminary BER, I've to put x amount of insulation between the rafters to get the roof u value within limits. My concern is that yes, i may get the u value within limits but what about the house air tightness?????

From reading here and researching on line, I came across the spray foam type insulation which if all the info on it is to be believed, should solve my insulation and air tightness concerns in one go. Only one company I have come across so far has the important BBA cert. I've not seen any with a IAB cert.

So, has anyone used the foam spray insulation to achieve what I want to achieve????? and most importantly, has anyone suggestions how to satisfy the roof breathing concerns my engineer has.

Thanks for reading and looking forward to all replies.

any certs ive seen for spray foam insulation, the thermal conductivity value has been 0.039... thats not great... its a kin to some quilted insulation, but worse than others...

basically, youd need the same thickness of 'spray foam' insulation as you wouls quilted insulation to meet minimum regs..

eg typically this would equate to 300mm between ceiling joists, and 250mm bwteen rafters...

do you have 250mm deep roof construction ??? wouldnt think so...

Syd,

Thanks for the prompt reply.

I am not sure how deep the Roof rafters are on my build; I'll check tomorrow.

I appreciate your comments about the foam thickness required to meet minimum building regs. The idea I had in my head was to blanket between the rafters in the foam thus achieving the Air tightness then use conventional insulation methods hand in hand with the foam insulation to achieve the u values I must satisfy e.g.:

Horizontal Roof: Glass fiber Insulation (Minimum u value 0.16 required)
Sloped roof area: Insulated plaster board flush against the foamed rafters (Minimum u value 0.20 required)
Knee Wall: Area behind knee wall; rafters foamed and then Insulated Plasterboard placed vertically.

The question still remains about the roof area been able to breath as I see no point in spraying tween the rafters then having to cut a hole in parts to allow air circulate in the small attic space that is above the bedroom area as this is a Dormer house

habitable rooms need ventilation to get clean fresh air to inhabitants, and to extract stale moist air to prevent condensation and mould growth.

Also, the roof needs to be ventilated over the insulation to extract condensation away from the timber construction.

The EOTA cert for icynene insulation states that the product shouldnt be used where condensation is a risk. Im most typical iriah construction condensation poses a real risk. Im not saying dont use it, but i would advise a full dynamic condensation risk analysis be done on teh construction.

the main reason spray foam (open cell of course)actually gets you better air tightness is simply down to bad workmanship with board insulation. The material doesnt make much difference.

Syd,

Fair play for the reply........ it is much appreciated.

I'll get the thinking cap back on ......... my main fear is that although i'll put in the insulation as per the BER spec done for the house and install the HRV as planned; i'll end up with very poor HRV performance due to Air leakage in the dormer part of the house. I know attention to detail should ensure a high standard but that in itself is a full time job.

Thanks again Syd, your help on thisForum is most appreciated

if you are definitely installing HRV then i would strongy advise the following.

get an air tightness test done before the wet plastering stage.
carry out all suggestions by air tightness assessor.
aim for at least a q50 = 5 level
do your best to reach this level...

could be the best 600-800 euros youll ever spend.

Syd,

Yes its definate that a HRV unit will be installed.

I will do as you have suggested above but could you elabourate on the wet plastering part; I presume you mean when 1st fix Electric and Pumbing is done and insulated plaster boards fixed in place.

Do you have any suggestions who to use to carry out an Air Tightness test?? No problem if you dont, I'll get oout the Gthrusty Golden Pages!!!!

Thanks again Syd.

Just a quick update, my rafters are 6'' / 150mm deep and spaced approx. 14'' apart. Will contact Kingspan & Xtratherm and see what they can recommend

Hi islanderre,
You never mentioned which type of foam you where looking at, it's important to know which one it is, sydthebeat seems to think it's Icynene, this is an open-cell foam, if it's a closed-cell foam then this has very different characteristics than the information you where giving, for one thing it has over twice the value per inch than open-cell, plus it's also a vapour retarder, I have worked with these materials in the US for many years and while I do work with it here this is not a hard sell, but if you don't know the difference between the foams you just get bad press.

V, Byrne,

Thanks for replying.

Would you recommend a particular type of Foam Type Insulation for my circumstances???

Currently researching the installation of a SIGA air tightness membrane and various types of insulation to get the U values quoted (MOY Metec, Kingspan, XtraTherm) above but I'm still open to the Foam Type Insulation provided I can get the appropriate certs. for my engineer who is only willing to sign off an certified goods.
The only Foam Type insulation I found which is certified is the Icynene which is open cell if I remember correct and the thickness I would require for the correct U Values would be too much considering my rafter thickness
The roof 'Felt' is Tyvex Supro and which according to its literature, insulation is able to be mounted flush up against it.

Hi islanderre
Agrement is mainly for new materials with no proven history, open and closed cell spray foams have been in use in the US and Canada for over 40 years now, the big chemical companies in the US like NCFI, Honeywell and BASF have documents on tests conducted on unvented attic's in all climates, I hope this helps.

Hi Islanderre,
I have come up against the same problem as you have as was wondering how did you resolve in the end as I have the same questions?

There are a few options available which allows the roof area to breath and provides a suitable airtightness level.
There are woodfibre(hygroscopic) insulations available which can be fitted between the rafters, which gives breath-ability to the roof structure. When you have achieved the correct insulation thickness and U value, you must apply a vapour barrier and finally the plasterboard.
You should carry out an airtightness test before the plasterboard is fitted. This allows you to calculate the airtightness level and also allows you to identify leaks and repair them with minimum disruption.
The airtightness level must be less than 7m3/hr at 50Pa to comply with current building regulations, but should be closer to 1m3/hr if installing MVHR.