Windows Before External Wrap Insulation Query

Quango Unchained

I know it is best to have windows installed and external wrap insulation (EWI) done at the same time.

We are on a waiting list to have EWI applied and don't have much control over the timing of when this will be done.

The windows of our early 1970s and window sills need to be replaced.

Is there a "standard way" of fitting windows in advance of EWI? Who would do this? And can the windows be installed weeks or months in advance of EWI? I don't think the fitters provided by the big window companies will do anything other than a bog standard install.

hesker

double post

hesker

There is a standard way and there is the right way.

EWI companies will say windows must be fitted first as it’s convenient for them and they don’t care about heat loss.

The right way is that the windows should be mounted in the insulation layer.

Do a search on here. One poster was lucky enough to have windows fitted same time as EWI and they built plywood or OSB boxes to position the windows in the insulation layer.

An alternative is to fit an insulated window mounting system made from dense EPS foam before fitting EWI. Google Compacfoam or Triotherm. WARNING: this stuff is not cheap.

It could even be possible to fit it before taking the old windows out although the window cills might have to be cut back flush to the wall. You’d want to be sure of your window measurements if doing this.

smyth79

https://www.boards.ie/discussion/comment/120893662#Comment_120893662

Do you think there is much of a difference in heat loss between the EWI overlapping the window frame (when the window has been moved out) and fitting EWI to the revel which overlaps the window frame (not moving the window out)?

Quango Unchained

From my basic understanding, you lose out in 2 ways if you don't move the windows out:

1. The insulation on the reveals is thinner (than the insulation applied to the main exterior walls)
2. The cold exterior frame is touch the interior wall (thermal bridge)

I'd also be interested in an answer to the question above.

On one hand "anything worth doing, is worth doing right" but on the other hand "don't let perfection be the enemy of the good".

hesker

I’m sure it has been modelled quite a lot and there are evaluations available online but I have not modelled my setup.

One setup has a very definite cold bridge and best practice is to reduce these as far as possible.

Quango Unchained

Just revisiting this. I found the document linked to below which has the following, what seems a sensible, practical solution, with some illustrations. Anyone any advice on this?

2 First windows, then insulation

2.1 Starting point

Generally, new windows are installed in the position of the old ones. This approach lowers investment costs because windowsills and any shading fixtures used do not need to be changed; the process goes quickly, and users are not bothered much. There are, however,

high follow-up costs. In the end, once the wall is insulated, it will have thermal bridges from installation, and solar gains are lower because of reveal shading. Additional insulation of the window reveals raises costs further; the application of exterior wall insulation and lower exterior aperture sizes due to reveal insulation can easily lead to an ‘embrasure’ effect, especially when windows are small.

2.2 Proposed solution

For the EuroPHit project’s 2015 Component Award “Windows in step-by-step retrofits”, the focus was on solutions that are as affordable and functional as possible over the window’s lifecycle with consideration of investment and energy costs for the entire service life. The result is surprisingly simple: The window, preferably with an integral frame (where the frame covers the casement), is installed flush with the exterior masonry, and the resulting gap is carefully sealed with a permanently elastic sealing agent (Figure 1). Well insulated Passive House frames are required for this situation; if standard frames are used, the temperatures at the interior window connection can be critical. Later, when the façade is renovated, the window frame can easily have insulation added to it. All other solutions turned out to be detrimental: If the frame is installed deeper in the reveal, the installation thermal bridge in the final state is much greater. Insulation of the reveal adds costs and increases reveal shading. A position within the future insulation level may be good in terms of installation thermal bridges and reveal shading, but installation in front of the wall leads to additional costs, and sealing off the resulting bays turns out to be difficult. In addition, the jury for the 

2015 Component Award found this “bay solution” to be unacceptable in terms of design.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://passiv.de/downloads/05_windows_step_by_step_retrofit.pdf&ved=2ahUKEwib9-T0xLyCAxXyZEEAHfd-DrMQFnoECB8QAQ&usg=AOvVaw0mrcwzDooNrFm3d83dbpM8