There seems to be more and more issues with retrofitting from single glazing to new higher achieving thermal glazing like double glazing.

Sean O’Sullivan has written an article in the Supplier Magazine which raises more interesting points, this time on timber joinery. Again we worry about the extra strain that these heavier DG units are placing on hinges and stays which are an important part of the window system. This is only a small part of the problem and I will now cover other problems relating to timber joinery that Sean has pointed out.

Glazing rebate to suit Double Glazing.

With single glazing it did not really matter if it was sitting in water, and usually it was due to putty cracking or even missing. With Double Glazing it is critical that the rebates will drain water away from the units otherwise they will break down causing the DG units to be in effective and there for the purpose they were designed for.

Unless the glazing rebate is designed specifically for double glazing, water can be trapped inside your glazing rebate and your double glazing units will sit in a “pool” of glazing rebate water. This will break down your double glazing units and can fail in a very short time. You will find that no double glazing manufacturer will warrant any units that have broken down due to sitting in a “pool” of glazing rebate water. Things like drain holes are required to ensure that the water drains away from the double glazing. With these holes come inspections. Customers will need to check periodically to ensure these holes are clear from debris.

If you are considering retrofitting in your timber windows, beware of windows that have not been specifically designed for double glazing. Even if they can take double glazing they may have been originally designed solely or primarily to suit single glazing and not well suited to take double glazing.

I read with interest the February/March 2011 BRANZ Build Magazine, page 72 headed “Supporting Heavy Windows.”

It raises a very interesting point. Coming from an industry that repairs aluminium joinery, I can understand a major problem is waiting to happen.

More and more consumers are looking at insulation which includes retrofitting with double glazing. This is going to double the weight of the glass which the frames may not be able to handle. When manufactured, it was designed for single glazing NOT double glazing and as all the corners are held together by one or sometimes two screws and a little silicone there is the potential for leaking due to the eccentric load from the heavier glazing.

As stated in the column:

“If insufficient vertical support is provided, this eccentric load from heavy windows can cause problems such as twisting of sill trimmers and window sagging, causing the joinery to leak.”

As we look more and more at the leaky home syndrome, is this another problem we do not need? Who will pay this bill when your house needs to be repaired?

Another statement reads:

“Recognising the possible problems, the Window Association of New Zealand (WANZ) markets a window sill support bar to carry the window weight back to the timber framing.”

Is this system being used with all retrofitting jobs?

Have any tests been done to show that retrofit double glazing is safe to be carried out in older joinery?

This is an issue that needs answers for the consumer!