Tommy’s Tips: Double Glazing for Period Houses


I was recently asked, what should I do? Should I fit double glazing to my period house to improve its thermal performance, or is it going to have a negative effect on its appearance, and is it going to be detrimental to the property value? A common question that I get asked time and time again!

You have to be very careful in your choice, or you could seriously affect the value of your property with a poor decision.

We generally have a vision of double glazing being white plastic (UPVC) or other colours, and are misleadingly told, that’s the end of maintenance, once fitted you can just forget about them! Well that’s simply not true! Any new windows will require maintenance, anything exposed to the weather requires maintenance, (including us!) a special paint’s even been developed for plastic windows, (and boy does that look great!)  That’s not even taking into consideration the more important issues of suitability for your property.

I have a general rule for period properties that I try to stick to, in an effort not to detract from the aesthetics, and distort the features in the original design.  That’s trade “like for like,” So if you’re going to replace something major, (or minor even) to your house, then have it made identical to the original, for example, if you have an original slate roof that requires replacing, don’t stick concrete tiles on because they’re cheaper, you’ll be putting extra load pressure on the timber structure, and the building generally, especially when the sandy coating wears off and they soak up the rain, doubling the roof weight, and dealing with all the problems that brings, all in order to save some money!

Take your time, plan it, research the materials, get the best deal, wait until you’ve got the money to do it right. If you need to make savings, keep the best of the old slates and re-fix them on the back elevation, and just buy new for the front elevation. Also try and avoid imitation slates, they get very brittle when exposed to the weather, and you have to strip half the roof in order to replace one. If you can’t afford the best slates which are Welsh, and are good for about 170 years, buy Spanish or Portuguese which are cheaper, but softer, and good for approximately 70-80 years. The roof will look much better, and you won’t be damaging the property.

Back now to the windows, I went off on a tangent for a moment!  If you wish your house to perform better thermally, and want to install double glazing then that can be done in the original material, whether wood or steel, because there is a new super thin double glazed unit available for this purpose, in-fact if you have a listed building, there are companies available that will remove the original sash’s, break out the old glass, then cut out a deeper rebate in the sash using a special jig and router, then re-glaze with a new super thin double glazed unit, so retaining the integrity of the fabric of the building!

I would add an important word of warning, beware inviting double glazed salesman into your home, if the deal seems too good to be true, then it usually is, choose your contractor from recommendation, and check out the quality of his previous work BEFORE he starts your work. Anything wood, always seek the services of a good quality joiners shop, who will make and fit bespoke windows for your home, rather than compromising your most precious asset, “your home”, with an unproven, environmentally negative, fashionable “faux pas” plastic windows in your beautiful period home!

Oh and one more thing, plastic is a much weaker material than wood or steel, so requires wider and thicker frames, and glazing bars, impacting considerably on the amount of natural light entering the room.  The room size was designed originally to correlate directly with the glazed area of the window, so ironically you could end up with gloomier rooms as a result of fitting new plastic windows! Which reminds me of a well-known actor who once said “Not a lot of people know that!”



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