Raised Heel / Energy Truss
user-901114
| Posted in General Questions on
My builder is about to order trusses. He is not familiar with raised heel / energy trusses. The bottom chords are 12in. How do I have him describe what I’m looking for to the middleman lumber yard guy, placing the order with boise??
I want to make sure they don’t mess this up. They are both “old school”! Which is mostly a good thing:)
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Replies
Fire the builder and find some who understands energy efficient building.
The bottom chords are 12"? Are you sure? Roof trusses are typically fabricated from 2x4s. Otherwise, you may has well stick build the roof.
I tried to hire you years ago but couldn't talk you out of the repubilic of VT! Too late to change now: The bottoms are 28ft 2x12's because it's a living space truss. To get R38, I need 11 inchs over the outside wall. Right now its 9 & 5/6". I'll have him build something inbetween the rafters leaving some vent space or change the truss design. Thoughts?
Stephen, ask the supplier. They will know what you want. I would go there with your builder if it is close by and work out the amount of lift you desire. 12" bottom chords are used for "room in the attic" style trusses. I like them and have used them when provided to me by Lincoln Logs Ltd. a kit home company.
If you need more help working out details of your plan Martin Holladay on this site is very helpful.
Dana on Greenbuildingtalk is a God of all things insulation and HVAC.
Robert Riversong prefers what he calls natural building. If you want to do any of that, like cellulose or straw bale, he is very knowledgeable. You may also get a lesson on what he thinks sustainable means. We all can learn about things we don't know if you can get through all that he posts on the subject.
Some sites to check
http://www.greenbuildingtalk.com/Forums.aspx
http://www.minnesotagreenhomebuilder.com/why-build-green-homes/energy-efficiency.php
and more from Ameris Company http://www.minnesotagreenhomebuilder.com/docs/Amaris%20Wall%20Section.pdf
Another way to insulate, build Bruce Brownell
http://www.aaepassivesolar.com/low-energy.html
Stephen, there you go with the info your supplier needs. Tell them you desire 11-12" depending on your vent chutes and you will be all set.
Where are you located?
Thanks for the info. I'm located in zone 6 new hampshire.
Stephen,
Any truss manufacturer can fabricate high-heeled trusses. You should have a minimum of 12" insulation space to the vent baffles if you want a settled R-value of 38.
But the minimum ceiling/roof insulation for zone 6 is R-49, which will require 16" height to baffles. I generally aim for R-60 in ceilings.
Stephen, you need to block off the area that you are trying to gain greater depth to hold back the cellulose right? Block with foam sheeting cut to fit and installed as you roll up your trusses. Foam them in place and done. You kill two birds with one stone and and have a tasty pigeon meal to boot.
The foam would give you all the R you desire with standard 12" bottom chord room in the attic trusses.
Sorry, what is a "living space truss"?
I've never heard that term before.
I think living space truss is an attic truss, rated for a higher ammt of weight and movement.
Talked to the builder. He thinks that by upping the bottom chord to a 2 x 12, having the 2x8 rafter end at the top of the 2 x 12, buiding tails rather than having the 2x8 rafters cut through the 2 x 12, and extending out two feet as previously discussed, that it would buy me the 11 inches of desired insulation depth at the outside wall with enough room for a vent.. I sketched it out and I just don't see it. By the way, it's a 9/12 pitch, not a 10/12.
Lucas,
An "attic truss" looks like this:
Stephen,
Don't talk to the builder, since he doesn't have a clue about energy trusses. Either go yourself or take the builder with you to the truss supplier and have them reconfigure the trusses to your satisfaction.
You may have to use something like this:
Robert, where did you get that pic? It's too small for me to see the details but it's what I'm looking for.. New Hampshire came out with a residentail energy code application(EC-1 Form) that I had to sign when getting the building permit. In it shows that in zone 6, they only require R38 if you maintain R38 over the outside plates. I will still go for R49 > R60 as funds come in.
I wish I could take off work and go to the truss sales guy with the builder. I will make them fax me what ever it is they propose.
http://www.mitek-us.com/Technical_Info/MiTek_Shape_Files.aspx
use closed cell spray foam insulation, you can get the high R-values with much less thickness.
Anonymous: spray foam is against my religion.
Don't trust any advice given anonymously.
I too am building an attic truss and am trying -in vain- to have my builder install raised heel trusses. How do I get him to understand? So frustrated. 12' bottom chord because it's living space, 8/12 pitch and I need more center height to add additional 7' doors.
Please help.
Rebecca,
Is there an architect on this project? Are there plans? Do the plans specify the use of raised-heel trusses?
Step one is checking out what the plans and specs say.
If there are no plans and specs, because you are just having a preliminary discussion with a builder, insist on what you want -- and if the builder balks, find another builder.
Trusses are rarely site-built these days; they come from a truss manufacturer. The truss manufacturer can build the truss any way you want, but the truss manufacturer needs plans and specifications to proceed.
There is an architect and plans. Currently the plans do not call for raised heel trusses. They are preliminary plans and this is the one item keeping her from creating the blueprints so we can break ground. Both the architect and the builder are basing their figures on the truss company standard. Do I just go straight to the truss manufacturer and ask for the specifications I want or do I need the plans for the garage for them to work off of?
Rebecca,
If I understand you correctly, you are the boss. You're the one who hired the architect, right? You need to direct your architect to specify raised-heel trusses -- and if you know the type of insulation you want on the attic floor, and you know your target R-value, you can specify the number of clear vertical inches between the top plate of your exterior wall and the underside of the roof sheathing. (Don't forget to add about 2.5 inches for the ventilation gap and the baffle.)
Once your architect is on board, the truss manufacturer will get the information they need.
If you feel that you need to educate your architect, you can contact a few truss manufacturers if you want, and ask their technical help people to provide you an example of what a raised-heel truss looks like. (Or you can just use Google Images to find lots of examples.)
Just for my own knowledge, is the depth of an energy heel measured from the outside top edge of your stud wall top plate to the baffle or the inside edge to the baffle? I would assume it's the smaller of the two measurements? Is there a dramatic energy penalty from thermal bridging if the two measurements are substantially different? I think double stud wall and a high pitched roof might lead to substantially different measurements.
Rick,
You can make measurements any way you want. I'm not sure what truss manufacturers require when these trusses are ordered; you can always ask your truss manufacturer.
To me, the important measurement is the vertical measurement from the top plate (measured at the exterior plane of the most exterior stud) to the underside of the roof sheathing. I suggested that this measurement should be depth of insulation + 2.5 inches.
If the vertical measurement is made at the interior plane of the stud, there won't be enough room for the full insulation depth at the exterior plane of the wall.
Since thin insulation at this location can be responsible for ice dams, it's a pretty important issue.