Potential hazard with angle lintel?
ElizabethRand
| Posted in Construction Techniques on
The structural engineer on a cottage remodel I’m doing has specified a steel angle lintel (drawing attached) where the horizontal part of the lintel is partly on the exterior of the cottage and partly on the interior. There’s a concern that in cold weather this will cause condensation to form which will damage the ceiling drywall.
Does anyone know of a way to avoid this? Forum members’ input would be most appreciated!
Replies
Liz
what was the engineer's response to this question?
thanks
Potential hazard with angle lintel?
Hi Calvin. I'm still waiting to hear what the Engineer says.
Climate?
Potential hazard with angle lintel?
Hi DanH. Canada, Ontario, cold winters (especially this year)!
Why does the window go to the ceiling?
Does anyone know of a way to avoid this?
Yes. Drop the window or raise the roof so that there is room to put a header in over the window to support the roof loads.
Do you really need the window to go up to the ceiling?
Potential hazard with angle lintel?
Hi Catmandeux. The clients want the window raised as much as possible which is complicated by a low soffit so I suggested a false dormer - gets rid of the soffit immediately above the window and allows the window to be raised. The Engineer says the steel lintel is essential for support but I'm wondering if this is going to more trouble than it's worth!
Other options to a steel lintel:
The steel lintel is a simple and relatively cheap option for supporting the roof load. A good engineer will usually design to minimize costs while still meeting the design criteria. You, as the client, need to make sure they understand all of your requirements, including archetectural or asthetics. Is you engineer aware of the condensation concern?
If there is condenstation, it means the cottage will be heated in winter, which then brings in the Ontario Building Code insulation requirements. These are specified in Supplementary Standard SB-12. The most common compliance package in that standard specifies min R24 wall insulation if the heating system is at least 90% efficient, otherwise R29. This usually means 2x6 walls with external insulation, or double 2.x4 walls. Both of these will allow the steel angle to be burried in the insulation, minimizing risk of condensation. Even better if an 8x4 lintel can be used.
Some other options: ( in somewhat order of increasing cost / complexity)
If dormer is wider that window, put a regualr wood or LVL header across the windows, and hang the trusses from that with brackets.
Use an I-beam. Weld on some hanger brackets to attach trusses
Drop the window to allow space for the header, install skylight as close to the wall as possible for increased light / view.
Make it a real dormer, using the wood beam as in (1). Use conventional framing to transfer roof loads to the trusses on either side of the window.
Raise the roof, using heel block on the trusses. Allows room for the wood header, and space for the ceiling insulation (R50)
Make it a real dormer, and extend window up into dormer.
Potential hazard with angle lintel?
Wow! Thanks Catmandeux! I'll pass these options along to the contractor who raised the issue. The Engineer seemed to think that the VB would deal with the issue but the contractor disagrees.
Many thanks for taking the time to respond so fully.
Liz
the short answer
Yes. Provide an adequate thermal break between the interior conditioned envelope and the steel lintel so that the dew point is never achieved at the surface of the lintel.
Potential hazard with angle lintel?
Hi Deadnuts. Yes, I thought that would be the solution but the contractor I spoke with said the vapour barrier would go on top of the lintel, not between it and the drywall. Is he all wet?
Is your vapor barrier also your adequate thermal break? I don't see it in your section drawing.
Potential hazard with angle lintel?
It is according to the Engineer. He says that having the VB between the lintel and the drywall will deal with the issue but the contractor I'm dealing with says it won't.
wonder if the contractor knows that he has either not installed the barrier as outlined in the engineers design and or is not sure how to do it if it has not been installed yet.
Potential hazard with angle lintel?
Good point, Mark122. It hasn't been built yet - no contract awarded yet. We're just at the stage of getting quotes and one of the guys wanting to quote asked to see the site and the eng's specs when he noted this potential issue. This forum has been a real help, raising some good points and possible solutions!
walk the talk
The engineer has not specified a thermal break (adequate or otherwise) in the drawing. It doesn't matter what he says. I've yet to see building specificatons approved on verbal descriptions alone. In fact, this alleged contract "award" is sounding more like a liabilty to me. Probably time to hire someone that can actually design according to best design and building practices. At the very least someone that understands code.