Thermal bridging and support wall

Hi All,
I was just wondering if anyone has any suggestions as to how to minimise the thermal bridging effect around a new support wall that's about to be built.
Basically my scenario is that the builder is about to construct a supporting wall (block on flat) in the middle of the house which will carry a beam at apex level in the roof. Therefore this structure of which about 4ft or so will be in the attic will bridge the warm house with the cold attic and I guess giving me heat in the summer when I mightn't need it but more importantly taking heat out of the living area in the winter.
My initial though after sleeping on it was to possibly slab the attic side with rigid insulation or am I being to fussy here. My overall plan is to externally insulate the building so the though of a heat conductor sticking up the middle of the house concerns me.
The attic itself is/will be well insulated at joist level.
Having said that, isn't this the same as having a chimney going up through the attic.

Thoughts/comments much appreciated as usual.

Regards
Fran

fran, if you are externally insulating then you may probably be better off insulating up the slope of the roof, and bringing the attic within the insulation envelope. That would be my preferred option. It means you can store some of your mech and elec in the attic as well.

yes, you are correct about the chimney being a cold bridge as well... i seriously hope you are not considering putting one in...

if you are perhaps you should look at building the chimney / support wall in either aac blocks (quinnlite) or in a foamglass product... at the points which it breakes the insulation level.

Thanks Syd, it's a big attic area (but low pitch) so bringing all the insulation up to rafter level is a big task. And I plan to pump it with cellulose at some stage. The Quinnlite block might be the answer though, thanks for that.
Do they have the same structural properties as the normal block?
Regards
Fran

ps the chimney is there already but about to be closed off (it's a renovation project). Maybe I'll remove it in years to come when I run out of other jobs.

Franm & Sid - you both seem to be well informed on insulation. I'm going to try to pick your brains if you dont mind. Tell me where to go if I am out of order.

I have just moved into an older house and want to put in insulation in the attic. We're not exactly flush with cash at the moment so I was wondering what the best value for money is for insulation? The attic is pretty much open plan and is easily accessible so I'm hoping it's not a big job. At the moment there is that old wire wool stuff. The attic is not floored, it's fairly large, prob about 40 sq metres. I dont mind doing it myself if that would be an option, so maybe I just need to ring around some insulation suppliers to enquire re price and options.

We're doing up the bathroom at the moment, there is one external wall that I intend to insulate while doing it. When we eventually get round to decorating and rewiring I intend insulating all the other other external walls. If you had any recommends what to use with this I'd also appreciate it.

Thanks.
David

David, do you want to use the attic as a room??? or just for storage etc??

what size are your rafters and attic floor joists??

Hi Syd. Thanks for the reply. Jut planning to use as storage. The distance between the joists is variable unfortunately, just been up to measure, between just under 12 inches and just over 13 inches. There is a depth of 4 inches between the joists where the insulation would go. There is plenty space to get around. The current insulation is not jam packed into the spaces between the rafters, there is some empty space so there is prob room for improvement re insulation but maybe it would not be worth it.

so at the moment you only have 4 inches to play with... you have a few options with varying degrees of workload.

1. install 4" of rockwool between the joists and another 6" over perpendicular to the bottom layer. This means however that you coulndt use the attic for storage because if you squash quilted insulation down, you loose its insulating properties.

2. do as above, but run new 6" joists perpendicular to below, and floor out. This means you can then use the attic as storage without squashing th einsukation

3. install 4" of rockwool, and reslab the ceiling below with a composite plasterboard, eg 47.5 board (35mm insulation and 12.5 mm plasterboard) . See kingspan kooltherm k17 boards.

4. install 4" of PUR insulation (kingspan, quinntherm, xtratherm etc) between joists, and use quilted insulation at eaves (this gives better u values,but wouldnt be my preferred option, because this puts at risk the integrity of the timber joists, assuming the roof spce isnt ventilated).

the above is only determined by what youve posted so far and is in no way a substitute for hiring a competent professional to advise you in the best way forward....

If space isn't an issue then I reckon I'd go with option 1 by Syd.
I also removed all the old (itchy) fibreglass and hovered the space (yes hovered). It made a huge difference to air quality up there not to mention getting rid of any other undesirable stuff up there such as mouse droppings etc.

Also it would be well worth getting a professional in to give an opinion. The best advice I received re this came from a BER assessor who was totally up to speed re the latest insulation products.
F.

Thanks for your advice guys. Re Syd option 1, I already have the 4", so I'd only need to got the 6" perpendicular to the joists I assume. I think I will go with this and then floor some f the area using your suggested approach in option 2.

I'll have a root around the web for BER people so I get good advice before throwing good money at it. Any suggestions re insulation providers welcome (Dublin area).