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insulating floor truss in crawl space

13K views 8 replies 6 participants last post by  AustinDB 
#1 ·
I'm looking at a job which will require removing all of the insulation in a crawl space and vapor barrier (plastic), airing it out and reinstalling. The floor trusses are 24" OC and about 16" deep (didn't measure). The R19 which was installed was installed vapor barrier down at the bottom of the truss-leaving an air gap between the insulation and the floor. Again, vapor barrier was facing down. The high levels of humidity in this space beaded on the kraft paper and the insulation fell down.

question-what is the proper insulation method in this case? my guess is non-faced against the floor held up by insulation rods. Is it improper to install kraft paper on the side not facing the conditioned space?

Any tricks for installing insulation in a situation as this where it will have to be tucked up into each truss.

Is there any merrit to the original installation where the insualtion was installed at the bottom of the truss leaving a ~9" air space between it and the subfloor?
 
#2 ·
#4 ·
It seems you left some important questions unanswered.

Is there water piping in that truss space?
Is there DWV piping in that truss space?
Is there HVAC ducting in that truss space?

Generally the vapor barrier belongs on the moist side. Insulating at the bottom of the truss leaves the web space heated. That space may need to be heated.

I don't think the original installation was a problem, excessive moisture in the crawl space may be a problem. The space may require mechanical ventilation or mechanical de-humidification.
 
#5 · (Edited)
:eek:Im glad its you and not me
Floor insulation is not common in
the south (cost vs savings thing)
and we dont offer it. In the last 15
years only one h o wanted it done
and did it him self.
As for the question- i agree with thom
and you may need to add more foundation
vents or some if there are none.
Allso you may need to take a good look at
the lanscaping and or gutter drainage. We've had
problems like that before.
 
#6 ·
I all ready identified the origin of the problem as being the downspouts and landscaping backflowing into the foundation entrance and vents and recommended not to have the insulation problem fixed unless the water drainage problem is fixed.

the link I posted addresses use of crawl space vents. It actually makes a case against vents IF there is air leakage into the structure (negative) whcih would draw outside air into the crawl space which would create moisture b/c of difference in dew point between outside/inside air.

Regarding Thom's comment, there is no need to heat the crawl space in our area as the temperature doesn't drop enough. Water and sewer connections are in the crawl space, but all grouped tightly (kitchen and baths are next to one another).
 
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