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This extra thickness needs to be accommodated in the rebate which has been manufactured to accommodate 4mm glass or on older box sash windows 3mm glass. This alteration to the rebate can come with problems, to begin with it may weaken the actual frame that the glass sits in i.e.: the opener or sash. Timber beading as opposed to putty has to be used to keep them secure, extra width may be required to cover up the edging around the double glazed unit. This can throw your eye towards this and can take away the originality of your period windows, also if you have original glass it may well be drawn glass as opposed to float which has a regular flat appearance this again can throw your eye towards this change of glass, and to be frank it doesn’t look right. Another consideration is the extra weight particularly with box sash windows this has to be counteracted with new sash weights which can be costly particularly if the pocket that the weights go into are too small to take the extra length of a bigger steel/iron weight and a lead weight has to be used instead.
You may have gathered at this point that I am no fan of double glazed units, single pieces of glass have an approximate life span of 800 years, double glazed units 15 perhaps 20 years before they ‘blow’ and condensation then becomes a problem in the space between the glass. Replacement really does mean replacement every 15/20 yrs! Indeed with modern plastic windows the guarantee more often than not does not cover the glass units, only the plastic and window furniture.
So what’s the solution? There are ways to overcome the inherent issues that you may be experiencing with draughts and maybe sound from outside, the first one is to perhaps consider investing in some thick curtains, they really do make a difference, or perhaps the fitting of acoustic and thermal seals, rubber strips that are fitted after a suitable groove has been machined on the edges of your openers or if you have box sash windows, brush seals fitted to parting and sash beads. Another viable option is secondary glazing, either fixed to the inside of the window frame, or sliding or the manufacture and fitting of a second window within the revel that opens inwards this option is common in many parts of Europe and was also employed in this country in the late 1800s in the centre of towns and cities.
The number one cause of rot, it cracks over time, usually starting in the corners, water gets in, and the damage starts. Water sits in the rebate where it has no means of drying out sufficiently, until next winter arrives, bringing more rain and, for good measure, a frost, which freezes the water between the glass and putty. This then expands, letting in more water, and the cycle repeats. These events will set in motion wet rot behind the putty in the rebate. If the damage is in the corner of the window, the joints between the bottom rail and stiles, mullions, and glazing bars start to suffer as well. It would be wise to check the putty on your windows once a year; it only takes five minutes, and if it is showing signs of degrading then get it raked out and a fresh bead put back in. You can tell if new putty is needed by seeing if there are any cracks in the putty or if it has come away from the glass, in which case you often see moss or dirt between the glass and putty.
Other causes of wet rot in openers can be as described above for window frames: poor quality paints, problems regarding the throat, shrubs, and leaking gutters.
Below highlighted in red are the most common areas vulnerable to wet rot.
An annual visual check and action on potential weak spots, coupled with a 5-7 year cycle of re-painting, will be sufficient to protect your timber windows for many years. The oldest windows I worked on were installed in the 1700s. They were ‘tired’ but because they had been included in a maintenance programme over the centuries (the windows were part of a church estate), they were in remarkably good condition.
As a matter of course I measure the moisture content of your windows, starting at the cill and moving up every 6” until I get a reading of between 12 and 18 percent. This will give me the information I need to asses the extent of potential wet rot areas. On average no more than 10% of any given window will be rotten, including the cill. Repair rather than replacement will be economically viable in all but the most exceptional cases of damaged of frames and openers. Of all the windows in a year that I assess, I see perhaps five percent that are beyond economical repair. In these few cases, it is cheaper for me to manufacture and fit like-for-like wooden replacements.
What is wet rot?
Essentially, it’s a fungal attack on timber that has high moisture content for an extended period of time. There are two main types: white and brown, with several less common types also in existence. You can easily identify both white wet rot and brown wet rot. The former has the appearance of fine threads and often a soft white tissue structure. This type is usually found between openers and cills or transoms. Brown rot appears as cracked cube structures, often brown and brittle, found on exposed timber and joints. Of the two, white rot is probably more destructive as sometimes the fine hairs can travel onto masonry.
Treatment is the same for both: cut it out and replace the affected area with new timber. If the spores from white rot have penetrated the brick this will need to be treated with an appropriate chemical solution.
There are very few instances where a window frame has become damaged by rot any significant distance above the cill. Such rare instances have four main causes: when water gets into the drip bar or the transom; when a closed opener sits tight on the transom leading to capillary action; when the opener loses the throating, usually the result of swelling, so someone shaves off the bottom rail so that the opener fits again and doesn’t put in a new throat; or finally when the throat has become filled with layers of paint over the years. There is a reason why the throating should be present all around the opener: it is to stop capillary action taking place.
The most common area where you will see rot is in the corners of the cill and in the first 6” on the frame jamb. It can be caused by the above mentioned faults, or by the pooling of water in the corners coupled with a poor paint surface. If the paint cracks at this crucial joint and water seeps in, the water has no where to go and no means of drying out, perfect conditions to allow wet rot to take hold.
Other causes of wet rot can be: poor quality paints allowing moisture penetration; painting timber with a high moisture content; timber of inferior quality (usually not applicable to pre 1970s frames); shrubs growing too close or against the timber; and gutters that leak.
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Giving your period windows a ‘birthday’ will save you money compared to replacement plastic windows. In my experience, I find that ‘replacement’ really means ‘replacement every 10-15 years’, as the plastic degrades and double-glazed units fail, costing you more money and costing the environment the problem of disposal. In contrast, correctly repaired and maintained wooden windows can last a lifetime or more, and are beautiful visually and to touch. Plastic windows just do not have the same aesthetic appeal. Scroll through my web site to see that I can tackle almost any repair. Feel free to phone me or contact me using the contact page.
Replacement of rotten cills to a former Victorian school, the grooves in the brickwork were made by pupils in the 1800s that used the bricks as a sharpening stone for their pencils, a marine primer was used to protect the new cills until a painter can finish in the desired gloss.
Refurbishment of a bay window…