Windows for extension

MarkZ

Hi,

We will be having an extension built later on in the year.

I have a question about windows and I wonder if anyone can help?

We like the windows from a particular danish manufacturer. However, the lead time on them is 8 weeks.

The build itself will be 10-12 weeks.

So, if we wait for the windows opes to be ready and then order, the windows will arrive 8 weeks later. This upsets the flow, since the builder needs the windows asap after the opes are ready.

Alternatively, we could order the windows based on the plans, and have them arrive after the ope's are ready. This seems like a good solution, but could we have difficulty fitting them? I would hate to purchase great windows, and then have them ill-fitting because of differences between the plans and the opes. We are primarily interest in avoiding heat loss - could a poorly fitting window affect this?

Any advice?
MarkZ

soldsold

If you only have a few windows, make up plywood forms (ie a plywood box wide enough to go across the cavity ie 300mm wide for a 100mm block, 100mm cavity, 100mm block wall) to make a box with no base and no lid. Make this box to the size of the openings you want. Build the blockwork tight around this box, and then remove the box when the blockwork is done.

Use diagonal bracing on opposite corners with 2x1's or so (inside and outside of the wall) to make sure the box corners stay at 90 degrees.

Make sure to allow for clearance around the window to allow for manufacturing tolerances and get a written guarantee of the minimum and maximum sizes the windows will be so you don't end up with big gaps to fill, or windows that are too tight

braftery

Hi there,

Soldsold's advice on the frames is excellent.

Prior to making the frames, I suggest you get your prices and choose your window supplier.

Get the supplier to give you, in writing, the opening dimensions that they require for the windows they are manufacturing for you.

In particular get them to give you details for the position of the cill head in relation to the vertical DPC line.

If your extension has doors, you will need to get door threshold details from the manufacturer, and you should check your foundation/sub floor/ raft with a laser level prior to block work starting to make sure it is level.

Having a door too high because the floor level is off is a very expensive mistake !

If you build the openings in accordance with the information that they provide then you are covered in case of any issues.

PM me if you need any more information.

Regards,

Brian

JuniorB

Also something to note.. You are planning to build later in the year but just in case it gets pushed back a bit ... check and see when they close for summer holidays - we've been caught out badly by windows not being ordered in time to get produced before the holidays and now lead time is closer to 12 weeks :mad:

braftery

I have just re-read your post and realised that no one has even addressed your final question.

The first thing to note is that an ill fitting window can be an expensive mistake.

If the opening is made too small for the window then you might not be able to use it at all ! This will mean re-ordering the window, paying for it again and causing the 8 week delay you are trying to avoid !!

If it is too small it is not quite as big a disaster but it can make it a little harder to fit and your plasterer will moan about the extra work to make the reveals bigger.

Making frames can make sure the opes are the correct dimensions and check to make sure they are square !!

Whether the windows are too small or the correct size, getting them installed properly (square, level and true) is very important. Not doing this will effect the window gear over time and will mean that doors will swing when you open them.

If it is properly installed (even if it is a little small) it will have no effect on Heat Loss. If it is badly installed all the valuable heat that your expensive low energy window is designed to keep in will simply pass out around the side of it !

There are EN (Euro Norm) standards for fitting windows that explain how it should be done. If you plan to fit the windows yourself or get your builder to fit them, then you should make sure you have seen them first.

regards,

Brian