Preventing thermal bridging around window reveals and doors

dbeermat93

I am looking for advice on preventing thermal bridging around window and door reveals.I am building a timber frame house with an external block leaf and a 50 mm air cavity.Some have suggested using cavity closers on either side of window like the link below
http://www.insulationdistributors.ie/downloads/thermal/quantum/Supafix%20Cavity%20Closer.pdf

But this would lead to deep window and door reveals and well especially with windows you would rather have more glass showing than the frame (in my opinion).what about using low preesure foam that plumbers use to seal up gaps? as for the lintel on top of window and sill on the bottom,would there be a significant thermal bridge above and below window here?

Regards

Dbeermat.

homewardbound11

Hi there,
I am at this stage of figuring out my options whilst awaiting frame delivery. I have been in contact with my frame company and looked at the options at hand.

-) Insulate internally at the frame perimiter but this gives rise to a condensation risk and is what is predominately used today. 20mm eps around the frame internally or insulated palsterboard.This did not remove the thermal bridge fully.
-) Use eps externally on the frame and plaster over to the window whilst internally using ther first option.
-) Use an insulated cavity closer that is also fireproof and works with frame/block builds with 50mm cavity. If you find this then please please let me know as I would like to see some draeings to put to my frame company.

Really the easiest way to reduce the thermal bridge and as far as i can see it (i am no expert) is to have the frame in the stud and use eps. The only risk in your case and mine (using cavity and block) is that if there is an issue with the damp proofing you would be more suceptable to leaks/damp than if the frame stud in the cavity.

I had alot of ideas but am still coming back to the original problem/ ideas. Anyone with some expertise here ?
Regards,

beyondpassive

You can eliminate the cold bridge by using softboard, such as 40mm gutex or steico outside, then where this wraps around the reveal to the window frame, use 25mm xps strips to get cold bridge free window installation. Use Therm 5.2 freeware to model heat loss.

However the big cold bridge is your rising wall. Would you be better using EPS formwork raft foundation and instead of a block outer leaf, use a renderboard clad ventilated cavity.

When designing timberframe housing, We generally specify 40 softboard on 225 studs with 75mm rails, cellulose filled with OSB inner racking board as vapour control layer with 60mm hemp filled services cavity inside.

DBeermat, are people still doing timberframe the way they did during the celtic tiger? What's your foundation and wall specs?

homewardbound11

Many thanks,
will check if i can do this.?:)

beyondpassive

Details attached as information only. Not for construction

very basic sketch showing the window installed from inside in the wide cavity and from the outside in the timber frame, ignore the membranes and dpc's, their incorrect.