Home Q&A: My terraced house is on a busy road. Is triple or double glazing best?
I have a terraced home on a busy road. What’s better for my home, double or triple glazing? How much more would I pay for triple-glazed units in general? Answer Right, so the first thing is to keep in mind that both double glazing and triple glazing can offer high energy efficiencies, depending on their specifications and the quality of the fitting. If you have single glazing right now, you can look forward to as much as 80% better thermal performance with double glazing installed. Double-glazed units have improved steadily in terms of their U-values, and in some instances, their performance comes close to that of triples, so it’s vital to go over the potential performance of each range in the same brand. Don’t be coaxed into a higher spend by declarations of how much energy you’re saving unless it’s fully explained. Comparisons with single glazed units or early units compromised by leaks and flagging frames — well, it doesn’t add up.If you don’t have your windows installed to a high standard, without airtightness right through the glass, the frame, and the reveal, they will underperform overall. Today’s minimum building regulation U-standard for new double-glazed windows is 1.4 W/sq m/K (the lower the number, the better). In 2009, the standard was just 2.2 W/sq m/K. Triple-glazed units today have dipped as low as 0.8 W/sq m/K for both the glazing and the frame. We should always try to exceed the minimum standards in U-values in all our insulation adventures, so here, triples generally win out, but there’s more, and in a street-side home, I would always recommend triple glazing.
If the difference in the energy saving is as much as 30%, it’s a no-brainer. Go with triples if you possibly can, even if it’s just on the colder and/or noisier side of the house. The warmth transmitted through windows can be surprisingly strong, depending on the aspect of the window or glazed doors. This heat, harvested from the sun, passing through the glass, is termed passive gain, and in a very big window, you will notice it in high summer without blinds on the windows. L-values relate to air leakage (look for Class 4 or up), and G-values relate to solar gain. Higher G-values of 0.6 can help to slightly warm south-facing spaces, but in a wall of glass, can lead to overheating. A triple-glazed window with a low-E coating to the middle pane, with lower solar gain compared may do better than a standard double glazed window. So, check the G-value of the windows you’re considering. Your sales representative should be able to go over this with you, considering larger windows facing directly south and southwest, for instance. To save a little money (the payback with new double glazing or triples is long) — householders mix up doubles and triples, with triple-glazed units placed on the cooler sides of the house (north and east), with double glazing reserved for the southern aspect where there is a little valuable solar gain — that G we talked about. Study the advice on your BER Advisory Report and talk to your OSS project managers if you’re involved in a deep-retrofit. The adage that triple glazing reduces light has some basis. With low-E, it’s around 10%, not perceptible to most eyes. One thing you will notice is condensation on the outside of the window. The window is cold because it’s so well insulated, and reaching a dew point, moisture in the outside air will appear, hazing the outside of the window for a short time. Kerbside situation To get back to your kerbside situation: Triple glazing has three pieces of glass, and that delivers two gas-filled voids. Those voids slightly improve the sound deadening from traffic noise and even conversational bustle on the pavement outside your home.This acoustic insulation creates a more comfortable, private and secure feeling when you’re sitting by the exterior walls by day or night, especially these days, when heavy curtains are coming down in favour of lightweight blinds. Specify laminate-glazed windows for a low db rating. Rationel Windows, for example, states: “If external noise is measured at 68db, equivalent to a very busy road, a standard double-glazed window will typically reduce this to 38db, compared to 27 db if acoustic control glass is used within the window. A decrease of 10db is perceived as halving the level of noise.” See rationel.ie.Triple-glazed units to the street side of a house don’t just offer a quieter window, with less sound transmission, they offer additional physical protection as they are simply more difficult to smash through and are detailed with formidable locking mechanisms. If you have added security concerns, an upgrade to 6.4mm with polyvinyl butyral (PVB) between the glass in a laminated glass can offer extra peace of mind.Keep in mind that installing quality triple-glazed units will demand 2mm x 16mm cavities, plus the glass (3mm x 4mm) and the frame, termed 4/16/4/16/4 in the industry. Swapping out standard 24mm or 28mm doubles to 44mm triple-glazed windows is more demanding. You can expect a little redecorating and a little plastering here and there to make good. Triples are physically heavier than doubles (around 50% heavier), so expect some reverberation if you wallop them closed in a timber-framed home. The difference in an entire window and French/patio door change between going double or triple (fitted) can be as little as 15% before associated builders’ costs. For superior thermal insulation (U-value) and almost fully deadening sound from outdoors, it’s a great investment. Every supplier will offer a different deal, but weighing up double-glazed units against triples, you may find the choice a highly competitive one — just check the depth of the units (16mm gaps are ideal), the U-values and the G-values. Your choice for top energy efficiency will likely be reflected in a higher BER, something that’s increasingly impacting the housing market.
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