Is thermal bridging through a solid wood door a big deal?
akhuntia
| Posted in Green Building Techniques on
We are going to be renovating our 1888 home to “pretty good” standards. I wasn’t planning on doing anything to the original solid wood front door besides refinishing, squaring up and rehanging (but I’ll pay attention to air sealing as much as possible – we are striving for <1.0 ACH). I am not so concerned about the energy losses caused by the thermal bridge but am a little concerned about creating a condition that causes the door to deteriorate (due to moisture or other reasons). What, if anything, could happen to the door?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Are you envisioning some scenario where tightening up the house causes problems for the door? I don't think that would happen without also causing damage elsewhere. Monitor rh and plan a ventilation strategy.
For the door - yes, weatherstrip as best you can (interlocking metal if you can get the tolerances right, compression otherwise), and a good storm door. Don't paint it a dark color if you're going to put in a storm door - the heat build up can be severe.
Thanks Dan. We aren't currently planning on a storm door but i will look into it. I was concerned of condensation issues due to the thermal bridge primarily. I imagined any condensation would just evaporate to the interior but wasn't sure.
Alex,
In extreme climates (Alaska, Antarctica) you'll get frost buildup on the door handle. Otherwise, there isn't an issue with condensation.
While Dan Kolbert suggested a storm door, energy research has shown that the energy savings attributable to the installation of a storm door are so small that the savings don't justify the cost of storm door installation. Most energy experts now advise, "Skip the storm door."
If it's a solid wood door it's U-factor is about U0.5, but a paneled front door with thin panels can come in at about U-1.0, and with seasonal dimensional changes of the panels due to humidity air tightness isn't assured.
With thin paneled doors there can be a rationale for a storm door. If the door gets much direct sun it should be single glazed to avoid warping the door with excess solar heating, but if it is predominantly in the shade it can be safe to use a U0.5 double-glazed door.
The value in storm doors is a much (or more) about comfort as it is about energy savings. Even a U-0.5 door produces a convective draft when it's cold outside.
Going with an U0.25 or lower insulated door would be the preferred option from an energy use point of view, but you'd be giving up some of that late19th century charm.
Here is a picture of my 1.75" solid wood front door taken on a cold January evening. I see lots of BTU's flowing through it.
Be sure to seal all six sides with primer at least if you cut or plane the door. Moisture that enters through the end grain of the stiles can wreak havoc with both the door and the fit to the frame (due to seasonal movement).
Had a cheap glass storm door when I lived in MN. It faced SW and in early and late winter we would often leave the door open just to allow the solar heat gain to warm the living room—made a significant difference. Also made the exterior paint on the door deteriorate nearly twice as fast (the surface of the door with sun on the glass in front of it could be almost too hot to touch).
I have been looking into the refurbishing of the door as I believe it might be the biggest obstacle to reaching our ACH target. I appreciate any suggestions but here is my plan...the doors are 6 panel 1.75" thick french door with 1 active and 1 inactive (48'x84")
1) dip and strip the entire door
2) run all edges through joiner until fully squared
3) fill all lockset cavities and hinge locations with solid wood (not filler) to prepare for new hardware
4) add a wood strip to create a step for weather stripping on outside edges. the custom jambs will have a matching step which essential provides 2 layers of weatherstripping around the top and sides
5) route and drill to install a multipoint lockset system on the active and inactive doors
6) install a metal interlocking threshold
7) install a compression weather strip or surface mounted magnetic astragal weatherstrip https://www.reeseusa.com/item/195C-195C
item 7 in general is my concern. I feel like the top and bottom of the astragal will be most likely to leak.
Any thoughts?
Thanks.