Thread: Crawlspace Insulation Soaked

I saw this house yesterday and the crawlspace insulation was literally dripping water. Here are the particulars:

- house has been vacant for two years
- hot water heat boiler was empty (no heat - for how long I don't know)
- crawlspace has concrete block walls with insualtion panels on walls
- concrete slab floor
- aside from the wet insulation, there was no water in the space (floor was dry)
- exterior grading around crawlspace walls could use a little correction out to about 1 foot away from the exterior walls but was otherwise not really bad
- no vents on the crawlspace side walls
- crawlspace was not open to the basement (access was through panel on rear exterior wall)
- insulation installed backwards on ceiling (vapor barrier facing was soaked in areas)
- no visible bathroom or clothes dryer vents exhausting into space

The insulation needs to be replaced so getting it installed in the proper configuration will be easily accomplished. What I'm wondering though is why the humidity level in that space was so high and what they can do to prevent it in the future aside from putting a dehumidifier down there and letting it run non-stop. Would the direction of the vapor barrier facing and the fact that the house may have had no heat for two years somehow created this condition? Are the insulation panels on the walls coupled with the improperly installed insulation on the ceiling creating a proverbial holding tank for humidity?

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- concrete slab floor
- aside from the wet insulation, there was no water in the space (floor was dry)

No vapour barrier under concrete floor will permit water vapour to enter the crawlspace area even though the concrete looks dry.

It sounds like they started to install a sealed crawl space and stopped before they finished. It looks and sounds like all they need to do is installed the heavy vapor barrier on the walls and floor, install a duct from the HVAC system into the crawl space (with a back-draft damper), and remove the floor insulation.

The insulation in the floor should be installed with the vapor barrier against the flooring, then the crawl space should be vented to the exterior. Otherwise they should remove the floor insulation completely and provide conditioned air to the crawl space.

They combined a vented crawl space design with an unvented crawl space design, then installed the floor insulation improperly causing this moisture/ condensation problem.

In either case get rid of the floor insulation it looks like its growing you know what.

Are you sure there is not a slow leak somewhere upstairs?

No leaks were noted and nothing visible that could be causing the condensation buildup. I believe water was off in the house for some time prior to the inspection. Adding conditioned air to the crawlspace will not be easily accomplished. The house has hot water baseboard heat and only wall mounted AC units in three 1st floor rooms (no HVAC duct work in the house). I did say that adding ventilation may be needed as they have to find some way of getting the moisture out of there and that all the insulation needs to be replaced.

Good info here
Building Science Insights
BSI-009: New Light In Crawlspaces — Building Science Information

The insulation paper will allow diffusion vapor, but hold liquid water.

Water source is from above the paper facing.

Suspect hydronic heat distribution/zone tube/pipe leaking/rupture(s).

The conditions warrant acquiring permission for a more invasive inspection and investigation.

What NC code says about closed crawl spaces...


R4Q9,5 Space moisture vapor control. Closed crawl spaces
shall be provided with a mechanical drying capability to control
space moisture levels The allowed methods are listed
below in Sections R4Q9 5 1 through R4Q9 5 5 At least one
method shall be provided' however combination systems shall
be allowed
R409.5.1 Dehumidifier. A permanently installed dehumidifier
shall be provided in the crawl space. The minimum rated
capacity per day is 15 pints (7.1 L). Condensate discharge
shall be drained to daylight or interior condensate pump Permanently
installed dehumidifier shall be provided with an
electrical outlet
R4Q9,5,2 Supply air, Supply air from the dwelling air conditioning
system shall be ducted into the crawl space at the
rate of 1 cubic foot per minute (Q 5 LIs) per 3Q square feet
(4.6 m2) of crawl space floor area. No return air duct from
the crawl space to the dwelling air conditioning system is
allowed. The crawl space supply air duct shall be fitted with
a backflow damper to prevent the entry of crawl space air
into the supply duct system when the system fan is not operating
An air relief vent to the outdoors may be installed
Crawl spaces with moisture vapor control installed in accordance
with this section are not considered plenums
R4Q9,5,3 House air, House air shall be blown into the crawl
space with a fan at the rate of 1 cubic foot per minute (Q 5
Lis) per 50 square feet (4.6 m2) of crawl space floor area.
The fan motor shall be rated for continuous duty. No return
air duct from the crawl space to the dwelling air conditioning
system is allowed An air relief vent to the outdoors may
be installed Crawl spaces with moisture vapor control
installed in accordance with this section are not considered
plenums
R4Q9,5,4 Exhaust fan, Crawl space air shall be exhausted
to outside with a fan at the rate of 1 cubic foot per minute
(0.5 Lis) per 50 square feet (4.6 m2) of crawl space floor
area. The fan motor shall be rated for continuous duty. There
is no requirement for makeup air
R4Q9,5,5 Conditioned space, The crawl space shall be
designed as a heated and cooled conditioned space with
wall insulation installed per the requirements of Section
R4Q9 8 1 Intentionally returning air from the crawl space to
space-conditioning equipment that serves the dwelling shall
be allowed Foam plastic insulation located in a crawl space
plenum shall be protected against ignition by an approved

thermal barrier

Dew point was reached.
Likely facilitated by the house being empty and swinging with the seasons.
Yeah, technically the insulation is in backward, but it is a very imperfect barrier. I bet if the house had been steadily occupied, the issue would be either nonexistent or much less.
jlmathis

Nick,
Solutions:
1) Heat space.
2) Seal floor and walls with membrane.
3) Add active (powered fan) ventilation

Originally Posted by Jeffrey L. Mathis

Dew point was reached.
Likely facilitated by the house being empty and swinging with the seasons.
Yeah, technically the insulation is in backward, but it is a very imperfect barrier. I bet if the house had been steadily occupied, the issue would be either nonexistent or much less.
jlmathis

I agree.

H.G., the moisture was not caused by a leak, anyone that inspects homes for a living would be able to see that a leak did not cause this.

Originally Posted by Garry Sorrells

Nick,
Solutions:
3) Add active (powered fan) ventilation

Bad idea in some locations. I would consult with local builders on that issue.
There have been cases here where powered exhaust fans have caused massive infiltration of moist air into the crawlspace from above. In my area at least, you can have plenty of cross ventilation with no need for a fan.
Dry heat, like an electric baseboard heater, works good here, but maybe not elsewhere.

Well little whipper snapper,Consulting for major lending institutions during the last two major RE crisises/"adjustments" and many thousands, not hundreds, of such improperly winterized homes vacant for several seasons. I was inspecting and reviewing projects and existing long before you were were potty trained.I speak from experience, which far outshines your own.Those I-joists or trusses are toast no mater what.As I said a more invasive investigation is called for.As far as your own brief "experience" doing anything "for a living" regarding inspection or evaluation, yawn, tadpole.

Originally Posted by H.G. Watson, Sr.

Well little whipper snapper,Consulting for major lending institutions during the last two major RE crisises/"adjustments" and many thousands, not hundreds, of such improperly winterized homes vacant for several seasons. I was inspecting and reviewing projects and existing long before you were were potty trained.I speak from experience, which far outshines your own.Those I-joists or trusses are toast no mater what.As I said a more invasive investigation is called for.As far as your own brief "experience" doing anything "for a living" regarding inspection or evaluation, yawn, tadpole.

I have told you that more fiber in the diet will help with that attitude.

Despite appearances, the visible areas of the joists were quite solid when I probed them.

For all you "wet behind the ears"
The first response was the correct response here. There is obviously a moisture source. Since there are no other obvious sources it must be evaporated moisture (vapor) coming through the porous concrete via capillary action. It's then condensing (turning back to a liquid) on the insulation surface. seal that concrete slab with a vapor barrier and the problem goes away. Fans, heaters, vents, dehumidifiers...all that sounds great if you want to manage moisture. But the first solution should be to stop it in the first place.
By the way...why is there a concrete slab under a house in the first place???

Originally Posted by Scott Patterson

I agree.

H.G., the moisture was not caused by a leak, anyone that inspects homes for a living would be able to see that a leak did not cause this.

This is a true statement but you should change the word 'would' to 'should' because there's lot's of guys out there trying to inspect for a living.

HG a wise man knows that age is not a guarantee of wisdom.

Originally Posted by Daniel Rogers

For all you "wet behind the ears"
The first response was the correct response here. There is obviously a moisture source. Since there are no other obvious sources it must be evaporated moisture (vapor) coming through the porous concrete via capillary action. It's then condensing (turning back to a liquid) on the insulation surface. seal that concrete slab with a vapor barrier and the problem goes away. Fans, heaters, vents, dehumidifiers...all that sounds great if you want to manage moisture. But the first solution should be to stop it in the first place.
By the way...why is there a concrete slab under a house in the first place???

Because it was the start of a closed crawl space that never got completed.

Originally Posted by James Duffin

Because it was the start of a closed crawl space that never got completed.

Why would a sealed or conditioned crawlspace need a concrete slab? very unusual.

Originally Posted by Daniel Rogers

Why would a sealed or conditioned crawlspace need a concrete slab? very unusual.

I've seen it a few times. Makes for a perfect floor....

H.G., the moisture was not caused by a leak, anyone that inspects homes for a living would be able to see that a leak did not cause this.

I wouldn't be so cock sure to make a statement like that, anything is possible given what we see as inspectors.

Based on the agreement that the crawl space is a sealed box the humidity cannot be dissipated, but you didn't note if the insulation is uniformly wet through out the space, as it doesn't in some of the pictures. Water infiltration through the windows or trim could run down the wall and end up in the insulation too. This could be a combinatorial error problem.
Fiber is always a good thing

Originally Posted by Daniel Rogers

Why would a sealed or conditioned crawlspace need a concrete slab? very unusual.

Every crawlspace built here in the last 15-20 years has a concrete floor. It is more or less mandatory. It is not really a slab, just a skim coat of a couple of inches thick over a poly vapour barrier.

The concrete protects the vapour barrier.

We can't be sure if there is a vapor (it's in the US) barrier under Nick's house, so it is all speculation. The boiler was empty. So that would not be actively leaking. But maybe the boiler leaked into the crawl, soaking the floor. Moisture had 2 years to migrate into the insulation, weird weather patterns in a closed up space.

A simple plumbing leak would produce a different pattern, unless it is exceptionally bad plumbing work. Not even multiple frozen pipes. But maybe a leak upstairs flooded the flooring, plank flooring, and water soaked downwards through OSB for 2 years? Too many maybes.

Hi, ALL &

A 'dead' indoor air-space is going to be TROUBLE...

Air-exchange is critical - as has been mentioned.

Poss. there is a leak, somewhere, but condensation is always BAD...


CHEERS !