Hi Folks,

How do I insulate a floor built on open wood trusses?  (Without busting the budget).

Rich

Just a guess, but radiant barrier (attic wrap - facing down) glued to strong foam board on the bottom and fill the remaining truss depth with cellulose? Then make sure you don't get a water leak/spill.

Rich,
Where are you located?

Hi Wes,

I just moved to Staunton, VA and I'm building a 20 X 24 workshop.

Rich

Will it be heated 24x7?

If this is over a crawlspace it might be the cheapest/easiest to pour the foundation walls using insulated concrete forms and either skip insulating the floor altogether, or in combination with kraft-faced fiberglass with the facing-side up, installed before you lay down the subflooring (provided your truss spacing is a standard fiberglass width.) Even low density fiberglass does much better in warm-side up configurations under floors than in cold-side up (the wintertime-attic scenario.) Unvented crawlspaces need a vapor retarder on the ground (mastic sealed at the edges & overlaps), and a small amount of conditioned-space air &/or mechanical dehumidification to keep the RH at 60% or under (70% for an absolute limit, over which the mold hazard simply explodes) but it's better from an energy use POV to seal & dehumidify them in mixed humid climates like VA than it is to ventilate them.

Rich,
For your location, I would suggest insulating the foundation wall rather than with floor system, as Dana has already suggested.
If the building is not yet built, ICF stem walls would be the ideal for this application. If the foundation walls are already built, then look at spray foam insulation on the interior of the wall. Or a simple (less expensive), solution would be to glue 2" of EPS to the walls.
One of these options, combined with a properly installed ground vapor barrier will work well for your needs.
(I'll let Dana provide the facts and figures, and just say that I agree with him, and his evaluation.)

     Thanks for the replies.  I should have mentioned I have a financial phobia of ICF, spray foam, SIPs, and the other "new fangled" (costly/DIY intolerent) building methods I see mentioned often on this site.  Basicly if it isn't in stock at Lowes, I'm not buying it 'cause it's too expensive, and I believe a smart person can build a decent building using common materials.
     I'd rather not use floor trusses (cost, dificult to insulate) but foundations are my weak spot, I'll have to sub it out, and I'm trying to keep it simple.  I'd really like to put the whole thing on piers (Bigfoot forms/cardboard tubes/concrete), but the lot is sloped and some of the piers would have to be tall and I think it would be a chore getting this past the local building code people (reported to be difficult).  So if I have a cement block foundation laid up and want to avoid wood trusses or center piers, I'll probably need a steel beam to span 20' to carry the floor load.  (Or would a LVL beam be cheaper)  I've never worked with steel beams.  Are these common/in-expensive?

thanks for any input

Rich
       

      

You might want to compare prices for LVLs, Glulams, and wide flange steel beams.  Be aware that LVL's do not have camber.  Glulams and wide flange beams are available with camber which is sometimes needed to offset heavy loading.

Common, but not at Lowes.

I wouldn't give up on piers so easily.

If all you have is a 20' span with standard loading, I joists will most likely be cheaper. Maybe 1/2 to 2/3 of the cost of a floor truss.

 

Bunt

ICF is fairly DIY-tolerant, particularly in short sub-1 story walls like you're talking.  It's not financially outrageous either, considering the amount of surface area you'd be insulating in a crawlspace height wall compared to the the entire floor.

But if you want to do it as a block-wall, price out what it would cost to do 2" XPS (R10) glued & furring-strapped to the inside vs. any technology for doing the entire floor at 1.5-2x the R-value (for similar performance, since it's typically far more surface area).

Steel beams are pretty common, but not cheap- it's usually not the cheapest way to go for low/moderate floor loads. Steel trusses can make sense for spans carrying massive slab-floors with strict flex limits/tolerances.

Rich,

I work in Staunton for a building supply company and I'm involved with ICF, so I should be able to help you somehow, if you haven't started already. Give me a shout at 540-910-2904. If I don't hear from you, best of luck.

renangle