# External insulation window reveals



## ciscojay (6 Nov 2011)

Can anyone give an indication of correct procedure regarding window reveals. Should they be removed if possible. My contractor has completed the frnt of my house, 2 window and front door and has not removed the reveals. Has placed 20mm insulation on top of the existing reveals adding now to the tunnel effect and encroaching on the windows to the extent that we had to check if they still open ok., Any advice welcome.


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## pudds (7 Nov 2011)

Sorry can't offer any advice but that sounds horrendous. Personally I don't see any reasons why the window reveals should be insulated for various reasons such as you describe, sounds like over kill to me.

This is just my common sense opinion.


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## ciscojay (7 Nov 2011)

Reveals are are insulated to stop the cold getting in as a matter of course! The question is, is it good practice to remove the existing revels to give mor room for the insulation?


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## onq (7 Nov 2011)

It sounds as though your builder has adopted a belt and braces approach in that he may have insulated over a traditional weathering detail.
Given that external insulation depends wholly on the external render applied to it for its weathering, this may be a good idea.

The building envelope is what separates the inner environment from the outer ambient temperature and weather.
It includes the floor slab, walls, roof(s), windows, doors and has support, weathering and insulation details.

A penetration of the building envelope requires detailing for weathering and to minimize cold bridging.
Penetrations which traverse structural cavities may also require fire sealing from the cavities.

The Technical Guidance Documents offer guidance on this, as do these approved details.

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These details are for solid and cavity walls.

Detail 2.20 shows the head with external insulation
Detail 2.21 shows the jamb with external insulation

These details only show external insulation.

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These details are for hollow block walls

Detail 6.19 shows the lintol with internal insulation
Detail 6.20 shows the jamb with internal insulation
Detail 6.21 shows the concrete cill with internal insulation

These details only show internal insulation.

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The requirement to prevent cold bridging through the reveals is present in all details.
I'm not certain you can mix and match per se, but the weathering layer in the case of the solid and hollow walls, regardless of the position of the insulation, is the external render.
The weathering function of the render is totally underplayed in these details, which centre on sealing the walling and insulation to avoid cold bridges.

The threshold details are not shown and these can be the hardest to get right.
With the prevalence of large bi-folding doors, they are very important.

These are from the DOE website.
They are not my details.


ONQ

[broken link removed]

 All advice on AAM is remote from the situation and cannot be relied   upon                         as a defence or support - in and of itself -      should       legal        action    be      taken.
 Competent legal and building professionals should be asked to advise in                           Real Life with rights to inspect and issue    reports    on     the         matters    at      hand.


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## lowCO2design (7 Nov 2011)

ciscojay said:


> Can anyone give an indication of correct procedure regarding window reveals. Should they be removed if possible. My contractor has completed the frnt of my house, 2 window and front door and has not removed the reveals. Has placed 20mm insulation on top of the existing reveals adding now to the tunnel effect and encroaching on the windows to the extent that we had to check if they still open ok., Any advice welcome.


this is happening all over the country, its pathetic and I sympathise with you. Unfortunately the way the grant system is set-up does not require any details to be agreed with the client or site supervision by a client rep. 

Ideally the windows should be adjusted (moved out) to overlap with the new EWI or if the client can afford the window should be changed at the same time to suit/ allowing more options.
the same issue often occurs at the eaves - where insulation is just butted up to the soffit and not overlapped with the attic insulation (allowing for ventilation also). at the ground - there should be at least a decent overlap with the ground floor insulation or better yet the paths lifted and the insulation continued to the foundations.

onq has linked the DOE details. although they are what the industry has to work with. they are outdated and do not deal with thermal bridging especially at the windows locations. whether this is due to industry pressure or just lack of knowledge, what does it really matter as these details are not enforced anyway by either your contractor or building control.
I should also add were waiting nearly two years for a BRE prepared 'Irish retro-fitting guide' so fingers crossed this addresses such issues more appropriately. or better yet the priory thing forces the gov to make some major changes in building control/supervision requirements


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## ciscojay (8 Nov 2011)

Nail on the head O2..It was something I was late in the day to think of and they'd started on the reveals B4 I got to discuss it. I've just today had a look at a couple of other jobs and they all seem to be taking the same shortcut. Suppose I assumed that ppl in this industry would be working to some sort of good practice. I do have a friend who works for another company and when I bounced the deal of him he automatically said the reveals should be taken off. Makes total sense as then you could decide to go with this min standard of 20 mm and keep the look of the window intact or then to add extra(10 or 20mm brings total to 30 or 40MM) and encroach on the window border.


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## onq (8 Nov 2011)

On possible problem with taking off the reveals is if/when the external weathering ever becomes compromised and admits water.
The standard reveal will be a back up detail to help keep water from penetrating the envelope at the opes (windows and doors).

There are no long terms studies of external insulation detailing in an Irish climate.
The render is subject to far greater cold and therefore retention of moisture than render on a typical uninsulated or poorly insulated outer leaf.
In a poorly insulated house, the heat warms up the outer leaf and the render protecting it - this cannot happen in a super-insulated house.
For 90% of the year this won't matter, but persistent zero or sub-zero temperatures will tend to freeze the render and cause spalling.

While the patent reveals may look clunky therefore, they may still serve as a useful backup.


ONQ

[broken link removed]

 All advice on AAM is remote from the situation and cannot be relied    upon                         as a defence or support - in and of itself -       should       legal        action    be      taken.
 Competent legal and building professionals should be asked to advise in                            Real Life with rights to inspect and issue     reports    on     the         matters    at      hand.


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## onq (8 Nov 2011)

BTW,

What kind of window cills are you having installed?


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