double glazing and external insulation

You don't aproach a single company in this case, otherwise you'll be ripped-off.
Contact a civil engineer who would detail what needs to be done and who'll controll the installation and sign for it.

There are companies that do both. I don't see the need for a civil engineer for this at all. Window companies expanding into insulation. I used one but can't remember the name. Post later when I get home.

I also used two other companies for external insulation and they were the best organized IMHO. Windows were no extra nor the insulation. There wasn't much on the convenience either so all I would say is get the windows done first.

dory wrote: »

I don't get this. I'm about to get external insulation and double glazing. So you're saying I should get the double glazing first, and then the insulation?

You'll need to discuss with the external insulation contractor. I don't know what adjustments they make to bring out the sills.

If your windows are not brought out the heat retained in your walls will escape along the external window reveal.

When I got a quote from an external insulation contractor this "recommendation" was buried in the ts and cs.

For better plasterwork and airtightness I would have thought windows should move first, but the sill complicates it.

Here's extract from the Ts & Cs (they emailed it to me)

[*]Ventilation
We recommend that the ventilation to the house be improved to avoid the problems associated with poor ventilation. Increasing the insulation in a house usually results in increased airtightness which can lead to reduced ventilation and potentially unhealthy conditions.
Poor ventilation can cause condensation and result in

• Poor indoor air quality
• Increased humidity
• Condensation on cold surfaces
• Mould growth.

We recommend the installation of a designed ventilation strategy which as a minimum should include humidistat controlled, pressure sensitive wall vents with a humidistat controlled fan extract(s). To ensure this ventilation is effective we would recommend internal doors be undercut to achieve a minimum 10 mm gap between the floor finish and the underside of the door to allow air movement from habitable rooms to the extract fan. If the extract fans are located in the bathrooms then the bathroom doors should be undercut to maintain a 15 mm gap
Other ventilation systems are available with varying degrees of efficiency and heat recovery and X Ltd would be happy to provide advice on the ventilation options suitable for this house.

[*]Cold Bridging


Windows and Doors
To avoid cold bridging at the window and door openings we recommend the existing window and door frames are moved forward in the walls and refixed in line with the external insulation as per the generic detail above. This avoids cold bridging which can lead to cold internal surfaces, condensation and unhealthy mould growth. Heat loss will be greater due to the cold bridging if this detail is not implemented.
Eaves Detail
The external wall insulation needs to continue up the whole of the external wall to form a continuous layer of insulation that meets the roof or attic insulation. This usually involves removing and replacing the eaves soffit to allow the insulation to be fixed above the eaves. If this work is not completed there is a significant cold bridge caused by incomplete insulation. We recommend this work is done to ensure the best results and to avoid the above mentioned problems caused by cold bridging.
Plinth Detail
The bottom of the external wall where it meets the ground is susceptible to exposure to water and mechanical damage as a "splash and kick zone". To ensure the edge of the ground floor structure is insulated by the external insulation we recommend an extruded polystyrene rigid insulation board is used to form a protective plinth to the mineral wool external insulation. This plinth is usually a minimum of 150 mm high , the "splash and kick zone", and the insulation is rendered to match the rest of the wall. The plinth is usually 50 mm thinner than the rest of the wall and can be painted a darker colour, as is conventional, so that it doesn’t show splash and scuff marks

A check of the Passive House guidelines would be helpful.