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under floor insulation

davejitsu's picture

House near water on beach on stilts. What is best way to insulate under house?

(post #115676, reply #1 of 26)

Didn't you already post this?

(post #115676, reply #3 of 26)

http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=115075.1

Looks like he is trying to makes us work twice as hard

 

 


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(post #115676, reply #4 of 26)

Perhaps he didn't like the first replies. 

(post #115676, reply #2 of 26)

if insulation were the only Q, then urethene sprayed on insulation is the answer, but surely you have some utilites involved.

Any way you could fully describe the situation or post a ccouple photos?

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #115676, reply #5 of 26)

So I assume that there is no insulation present currently, or else, what's the question...Stuff fiberglass in your bays and seal off bottom with 1/4 or 3/8 treated ply wood,seal all your cracks, than paint to match....that's what I'd do...Of course someone mentioned earlier spray foam...That probably would be your best option, but that stuff is ugly, however if your "stilts" (vsm's for those who know) are short enough, you might not see the foam...got pics? your description is as vague as a blind man describing the color orange....

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(post #115676, reply #6 of 26)

Sorry about the double inquiry I did not think first went through. joist are 24 on center. House just about 100 feet from water Stilts are about 24" tall. Fiberglass most likely best But pvc drain pipes hang down And they freeze. House not meant for year round occupy. Iwonder if pipes are foamed if that would help.

(post #115676, reply #8 of 26)

I wonder if pipes are foamed if that would help.


Not unless there is constant flow in them. Insulation only slows down the heat transfer process; it does not create warmth.


To keep those pipes from freezing, you're gonna have to close in the crawl space with an insualted skirt--something like XPS foam board that can take being flooded (since I gather this place is subject to occasional bouts of high water)--and put some heat down there. If the insulation on your perimeter skirt is good, you won't need much heat. A few 2500w electric baseboard units screwed up high enough that they themselves won't get flooded oughta do it.


Oh, yeah: provide for summer ventilation of that crawl space when you close it in. If you keep it sealed up in summer, you're gonna get all kinds of interesting moulds and fungii growing on your undercarriage....



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foolish men call Justice....


Dinosaur

How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....

(post #115676, reply #12 of 26)

Creating a perimiter with foam sounds like a great idea. House around 600 sq ft around base and 24" off ground. Should foam be backed up with plywood or is it strong enough on own? Wind is also a factor. There is noe about 2" of frozen water under house.

(post #115676, reply #13 of 26)

"There is noe about 2" of frozen water under house."


Which is why the perimeter insulation is not such a great idea for shore locations. There's just no way to keep the ground under the house dry enough. And boxing it in will just make matters worser.


Again, that's why it's on piers.


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115676, reply #14 of 26)

Ok It has been suggested to do an energy audit on house. Than see about insulation in walls. Now spending $1000 pr month on heat bill. If we insulate under house. What are your thoughts on Azec instead of marine plywood to cover. Than electric pipe wrap for exposed pipes? Maybe foam board south side of house along perimiter to help block wind.

(post #115676, reply #15 of 26)

How about just as a wind block on one wall south side?

(post #115676, reply #16 of 26)

Wind block shouldn't be a problem. But I'd shy away from sealing that space up.


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115676, reply #17 of 26)

In sealing space up Your saying no perimeter? Just under house To protect insulation Am I right? Makes sense due to flood. Thank you for patience

(post #115676, reply #20 of 26)

I'll preface this by stating I have never done any shore construction, so others here who have may well tell you I'm all wet (no pun intended) -- and they'll probably be right. But . . .


The typical way to insulate a crawl space (which is sorta what you have) is to seal off the perimeter and insulate the perimeter walls instead of insulating under the floor. This is most often a better solution for a number of reasons, but mainly because it usually takes less insulation to get the job done since the floor area is often greater than the area of the perimeter walls. It also makes it easier to deal with HVAC, plumbing, etc.


However, your case is not typical. Your house is on the shore, where there is occasional storm flooding and, more likely than not, a high water table. Your house was built to stand above the expected flooding, not hold it back. (Holding back the ocean is, after all, almost impossible. <G>) Erecting a perimeter wall defeats this scheme and will likely only serve to trap moisture under the house where it can more easily wreak havoc with your floor framing. I think your best bet is to let the piers on which your house is built do their job to let the water move in, and more importantly out, from under your house as it will, but carefully insulate and seal the flooring system. Although it's not the cheapest (by a factor of about 3), foam is best for this since it pretty much completely seals the cavities and getting it wet really doesn't affect it, unlike FG or cells which can be pretty quickly ruined by water. You need to think about the floor kinda like a roof on the bottom of your house. You don't design a roof to keep the heat, cold and rain from hitting the roof, just to resist allowing them into the structure.


If it wuz me (and it ain't), I'd be talking to local insulation companies to see how they typically handle this type of construction in your location -- there must be a bunch of houses similar to yours in your area. And talk to some of their customers to see how satisfied they are.


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115676, reply #18 of 26)

"There is noe about 2" of frozen water under house."

Well that changes a lot! Is they a way to provide drainage to stop this?

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #115676, reply #19 of 26)

"Well that changes a lot! Is they a way to provide drainage to stop this?"


I saw in a cartoon once where they pulled the plug in the ocean and it drained nicely. ;-)


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115676, reply #21 of 26)

One thing the insulation companies will not do is consider protecting your exposed wood from the problems you mention. If there is any chance your insulation project will trap moisture, consider oiling the wood surfaces. For this, I would use a non-hardening oil. You can buy it from places like Chevron. It's called shingle oil. In a pinch, you could use cheap motor oil.

First, WEAR A MASK. You can oil with a brush, roller, pump-up garden sprayer or a spray gun. In any event, you want to thin it. I'd start at 25%, but thin more in colder weather. This allows deeper penetration and allows you to use things like pump up garden sprayers. As long as the wood will absorb oil, it's fair game to add more. Well oiled wood won't take on moisture and won't rot. The thinner (paint thinner, turpentine or Naptha, whichever is cheaper) will evaporate and leave the oil behind. In a few days, there shouldn't be any notable odor.

Keep in mind that anything you buy that uses the words "sealer" on it is normally going to harden. As such, it wont expand and contract with the wood and will crack and allow moisture in. As such, old technology is probably your best bet.

When we insulated the floors of our damp basement, held it in place using tig welding wire and plastic washer nails. Then we used drain fabric to protect it. That allows it to breath.

That which I least want to do is oft that which I most should do. And I can't afford cheap.

(post #115676, reply #22 of 26)

I would have never thought of oil seal like that! Wow what a great idea Thank you

(post #115676, reply #23 of 26)

No house just close to water a pass through cretaed by piers

(post #115676, reply #24 of 26)

Here is my understanding propose both fg and foam insulation let customer decide on money. Close with oil sealed plywood. Create wind break on south side leaving space for water to pass Using xp foam Or perhaps azec. Wrap pipe with electric tape or provide a heat source. I hope I got that right. And thank you to all for your patience with my poor typing skills. Also have energy audit done.

(post #115676, reply #25 of 26)

If that means that this is in a flood zone, then any underskirting has to be designed to be flow though, so typical perimeter insulation as an underskirting would be a poor choice. Also, fibreglass would probably end up wet at some point and need replacement, so I would highly recommend using a closed cell spray on foam insulation.

This thread is a good example for other readers here how important it is to know and understand the many variables that go into a decision of any kind in the building and home improvement process.

best of luck to you

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #115676, reply #26 of 26)

I fully agree on foam I believe that any type of skirt will cause a problem. I am thinking that foam vs Fg is up to budget. Will propose both. Plywood to cover should shield. With a preservative (oil) and caulked seams. Than heat source for pipes Wrap is electricans choice. Also I am adding energy audit for customer review. I dont believe there is any insulation in walls ( just a guess) You guys are all top of the line people. I will let you know how it turns out If I get job.

(post #115676, reply #10 of 26)

Your first mention of it being up on stilts created a picture for me of 5-9' up in the air. Since it is only 24", I agree with the idea of underskirting it and insulating the perimeter

 

 


Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!

 

 

Oh Well,

We did the best we could...

(post #115676, reply #11 of 26)

"Fiberglass most likely best "


Well, FG is most likey "cheapest", but not best. That house is on stilts for a reason -- water gets under it from time to time. When that happens, if the FG gets wet, it's worse than worthless -- in fact, it's a liability. Foam is best, covered with marine ply to protect it from damage and critters. However, "best" often equates with "most expensive", and this instance is no exception.


Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115676, reply #7 of 26)

Obviously by crawling underneath.

 

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(post #115676, reply #9 of 26)

Poly foam, which would also provide additional flotation when sea level rises.