Thermal bridging detailing

Quazzie

AS most of you know I'm well under way on my self-build and at the moment I am doing up detailing for Airtightness and Thermal Bridging Prevention but I've come across an area I don't know how to get around.

The drawing attached shows an eaves detail, of a storey and a half house, I will be using which eliminated most thermal bridging except in the path Rafter>Wall Plate>Inner leaf. Has anyone got any suggestion how to over come this? Or any other details they think can be employed to overcome this? I'd really like to keep thermal bridging to a minimum.

P.S apologies for the crudeness of the drawing, I had to knock it up on 2000LT

RKQ

Difficult one really. Always a difficult detail.
I think it will be very difficult to get the wall insulation cut around each rafter, as shown, to form a snug fit.

sinnerboy

Try insulation over rafters not below

Poor Uncle Tom

Between and below, maintaining your air flow gap over.

sas

A friend of mine is building a certified passive house. His house is being supervised by the Passive House Institute themselves.

He is doing exactly what you have suggested for the roof i.e rafterloc between rafters and insulated slab underneath. The PHI are happy with this detail.

The only difference is his walls are block on the flat with an external insulation system. This is irrelevant though.

So in a nutshell I think you are being overly concerned. It can be improved if you insulated over the rafters as sinnerboy has said.

Quazzie

sas wrote: »

The only difference is his walls are block on the flat with an external insulation system. This is irrelevant though.

This is basically what I am doing except I've a 100 outer leaf that is basically just a base for render rather than render onto external insulation. I know my insulation thickness is limited to 100/110 because of this but I'm fairly happy with this.

sas wrote: »

So in a nutshell I think you are being overly concerned. It can be improved if you insulated over the rafters as sinnerboy has said.

its not something I've considered but I might look into it and see how financially viable it is.

ardara1

Google Enhanced Construction Details from EST - 30mm insulted lining to achieve PSI value thru' the junction of 0.04 - easily achieved.

Jimbo

Slightly off topic but what company does 100mm cavity PIR insulation?

ardara1

jimbo78 wrote: »

Slightly off topic but what company does 100mm cavity PIR insulation?

Kingspan, Quinn, Xtratherm & Litepac all do 100mm - but back to the original topic - the better the U-value in the vaue - the worse your detailing loses gets - how will you address this? Have you increase wall tie size/quantity to suit the wider cavity? This is also detrimental to wall U-value.

Quazzie

jimbo78 wrote: »

Slightly off topic but what company does 100mm cavity PIR insulation?

Xtratherm do it here in an exterior insulation(not 100% if this is suitable for a cavity), or here in a combine 50mm +50mm board*.


*This can be achieved successfully in my build as I intend to build the 215 inneer leaf first, then install insulation, then build the outer leaf.

thunderRoad

Quazzie,
Trying to come up with a solution for the same problem,
have you looked at multi-foil insulation, if it does what they say, it would allow you to use slightly thinner rafterloc, it can be raised up from the underside of the rafter so that u wouldn't have to notch it around the wall plate,
and then put the multi-foil on the underside of the rafter
maybe continuing the wall insulation up to flush with the top of the rafter, so that the rafterloc could be more easily cut to fit against it.

seen the detail for it here
http://www.just-insulation.com/pdfs/multifoil/Thinsulex/Thinsulex_Silver_Install.pdf

would be interested in hearing other posters opinion on this
maybe this idea has no merit other posters here would be alot more qualified to judge!

thunderRoad

sorry, wall insulation continued up to the top of the rafterloc, not flush with top of rafter, to allow air flow to roof.

hope post is clear, not very good putting thoughts into words!

Quazzie

thunderRoad wrote: »

Quazzie,
Trying to come up with a solution for the same problem,
have you looked at multi-foil insulation, if it does what they say, it would allow you to use slightly thinner rafterloc, it can be raised up from the underside of the rafter so that u wouldn't have to notch it around the wall plate,
and then put the multi-foil on the underside of the rafter
maybe continuing the wall insulation up to flush with the top of the rafter, so that the rafterloc could be more easily cut to fit against it.

seen the detail for it here
http://www.just-insulation.com/pdfs/multifoil/Thinsulex/Thinsulex_Silver_Install.pdf

would be interested in hearing other posters opinion on this
maybe this idea has no merit other posters here would be alot more qualified to judge!

There is no Multifoil insulation that that is IAB approved therefore any benefit of it is not certified for use in Ireland and can not be used in the calculations of the BER, or towards compliance with Part L. Maybe this has changed recently, if it has then I'll gladly stand corrected

I had considered using this before but without certification and comprehensive evidence of how it works in combination with other materials I decided against it, but that was just my personal choice, based on basically a toin coss about what information to believe and follow.

This certification might change in the future, but until then, I'll personally be staying away. Maybe others here might or can refute what I'm saying, or point us in the direction of a valid alternative.

davidoco

Regarding the rafterloc, from experience I put in 100mm in room in roof. While the 565 does allow a 10-20mm flex laterally the boards in each pack can vary in supplied thickness from 550 up to 580. Those boards in the 570-580 range were difficult enough to fit without having to fit them and then slide down towards a cavity. I was working with a cut roof.