How To Slam The Door On Winter With DIY Glazing

French doors might be fashionable, but along with glass sliding doors they’re an open invitation for winter to walk right into your house. Here’s how to seal them up and refuse to let cold weather in when it comes knocking.

French doors are a lovely thing to look at and a terrible idea for much else, except moving furniture. Having vertically pirouetted a couch through a conventional doorway on a few occasions, it’s appealing to march through without damaging the furniture or the frame.

In my opinion, the only thing worse is a glass sliding door. My Mum once tried to walk through one because it was so immaculately clean, and it caused her a significant neck injury.

Glass sliding doors are both novelty oversized and badly sealed, but they’re cheap, so Aussie builders love them.

Okay so maybe a glass sliding door is handy if you’ve spent $35k on a paint job and need some interim storage space.

Sealing Windows Makes Sense

As we wrote previously, a single pane of bare glass can gain or lose up to 10 times more heat than the same-sized area of uninsulated wall. Adding secondary glazing is a real winner when you’re trying to make best use of your solar power.

Having put a removable pane of perspex on my bedroom window, and used it to cover the entire sash window opening, the first thing I’ve noticed is the reduction in noise. That was worth the price of admission alone, so the thermal and draftproofing improvements are a bonus.

French Doors Are Fashionable But Not Flash

When I pointed a thermal camera at these two, it was vividly apparent that not only was the glass really cold, but the lower infill panels were also frigid. I decided to enlarge the perspex panels I was ordering for these traditionally built timber doors in order to cover the thinner timber.

While I’m more concerned with function over form, a 25mm white frame on this timber would look pretty confronting, so I’ve elected to use some off-the-shelf pine moulding, basically because it was the only available profile that had a 4mm recess.

I did consider fixing these strips with screws, so they could be removed to clean the window, however your average hardware shop simply didn’t have something small, long or attractive enough. Besides, you’d have to remove at least two sides to release the pane.

Get your square, pencil & blue cardboard sword when setting up.

The Finer Points

If you fit the lower moulding first, it’ll be less visible when you make mistakes and need to reposition it.

Small errors on the short side are magnified by the long side as seen by the gap next to the door bolt.

The aim of the game is to get the new pane installed looking square to the nearest straight edge, which may not align with any of the other parts of the door, depending on how it was trimmed when they hung it originally.

Once the bottom edge is true, add one of the sides and use the new pane as a template to get the frame square and the long flexible moulding straight.

I found the removable film made a great notepad for measurements and saved scratching the plastic.

Remember that long flexible Perspex sheets are easy to snap in half though. Some suppliers don’t actually saw the material to size, they instead score the surface and snap it, leaving a sharp and often less consistent edge.

The blue arrow shows how nails are left proud so they can be removed if need be. Red highlights the expansion space.

Perspex needs room to expand so give it 5mm of space for every metre of material. Seeing as timber does breathe, I don’t want a perfect seal here, but so far there’s been no condensation problems.

Peel the edges of the paper carefully before you position the mouldings and nail them down, then enlist help to remove the rest

Proof In The Pudding

Once the Perspex pane was in place the thermal camera showed a 3.5ºC difference, you could feel it standing in front of them.

The bottom panels measured 20.6ºC and 22.8ºC.

Heading outside I found the external glass was 14.1 ºC vs 16.4ºC,.

Another issue that needs investigation is above the doors. There’s an external vent in the weather boards and a penetration where the split system air conditioner plumbing goes through the wall. One or both of them is leaking heat as indicated by the 20ºC  reading.

Thermal cameras show all sorts of things you wouldn’t otherwise see.

There’s More To Do

I cursed wrote about these doors last year and I’m pleased to say the improvements I made then have proven durable enough. However there are a few details to fix up.

Self-adhesive weather strips don’t always stick to everything, so in places I’m going to try a little Sika 11FC to fix them.

Apologies if mirroring one of these images makes it look weird but you can see where the stips are peeling off.

The best tip (pun intended) in this entire article is these Sika nozzles with a screw lid. The thread is fine and easy to strip if you’re ham fisted, but they beat the sh!t out of any kind of tape, nail or screw you would otherwise bung the nozzle up with. These should be made law to prevent waste of expensive sealant.

I cannot recommend these nozzles enough.

Using EPDM strips on the door frame has been more successful. This style has a hollow section to give it perhaps 5mm of compression but if your doors are a very close fit they may not close properly once the strips are in place, or you might find the door itself bows out of shape if you manage to slam it shut.

When fitting these strips, remember they tend to peel off when subjected to a sliding or wiping motion. It’s much better when the surfaces push together.

These strips can get wiped off in the corners but so far this has worked well

I’ll have another crack at these two with some more secure door bolts and better sealing belts, but unless we machine a rebate for a rubber strip, this will always be a stopgap affair.

The wiper on the outside was the last occupant’s idea while the foam strip inside was my attempt.

Tune In Again

Next time I’m going to have a crack at some windows that don’t lend themselves to secondary glazing. We’ll use some CAD¹ to make up a window sill and then add enough framing to make the perspex stick.

Hopefully we can make the house a bit more liveable by keeping the drafts at bay and help you identify the places your house can use improvement.

For more on improving the thermal comfort of your home through winter, read my guides on some simple cheap hacks, tips on insulating windows, and maintenance of your reverse-cycle heating.