closing the underside of the floor ?

henderson · September 03, 2011, 08:23:51 PM

I'M WAS WONDERING WHAT PEOPLE ARE DOING TO CLOSE OFF THE UNDERSIDE/CRAWL SPACE AREA OF THE CABEN THAT ARE BUILT ON PIERS. INSULATION ,PLASTIC..? HOW ARE YOU KEEPING THE COLD OUT.

astidham · September 03, 2011, 11:12:55 PM

I will be adding 2" on closed cell foam to mine!

September 04, 2011, 11:58:19 AM

We've written about different ways of doing this.

I like the get all your under floor plumbing , wiring , gas piping needs done first.

Then insulate with fiberglass batts , then apply Tyvek / Typar to the underside of the joists as it breathes so should allow things to off gas / keep drying / allow moisture that escapes the inside to disperse , then apply 1x2 batten strips every 2 ' OC to hold the building wrap in place.

The battens could be screwed on because some day you're going to want to either replace the building wrap as it wears out, maybe a 20 year life expectancy , my guess , or your going to need to access the joist bays and IF you screw the batten on you'll be able to remove them and then re-install them undamaged .

This of course insures you'll NEVER have to remove them as you set it up to be removed

LOL.

Then once you're done with that close off the under side with Hardi cement board the stuff we sue f0r soffits , it's vented and you can put dirt right ny against it to keep rodents for getting into you crawl space, and yes you'll need to use pressure treated lumber to build pony walls to nail te Harid soffit material to.

So you create your own "concrete" crawl space in essence.

G/L PEG

DirtyLittleSecret · September 04, 2011, 03:07:28 PM

Finish plumbing/electrical/gas lines, stuff R30+ insulation with hangers/lines, staple up some Tyvek with slits to enhance breathability, then finish with 1/4" mouse/squirrel wire to keep furry critters out. At least that's what I did.

considerations · September 04, 2011, 10:36:54 PM

"Finish plumbing/electrical/gas lines, stuff R30+ insulation with hangers/lines, staple up some Tyvek with slits to enhance breathability, then finish with 1/4" mouse/squirrel wire to keep furry critters out. At least that's what I did."

As did I

September 05, 2011, 12:03:51 AM

I'M A LONG WAYS FROM THIS POINT. STILL IN THE PLANING STAGE. BUT I WAS THINKING R-30 THEN WRAP WITH TYVEK AND USE LATTICE. BUT I LIKE THE 1/4 SQUIRE WIRE IDEA TOO. THANKS FOR THE HELP, JIM HENDERON

Danfish · September 05, 2011, 08:26:21 AM

Interesting that Tyvek and Typar house wraps have been used on the underside of floors. I seem to recall reading somewhere that these house wraps are recommended for vertical installations only.

PEG688 · September 05, 2011, 11:18:04 AM

Quote from: Danfish on September 05, 2011, 08:26:21 AM
Interesting that Tyvek and Typar house wraps have been used on the underside of floors. I seem to recall reading somewhere that these house wraps are recommended for vertical installations only.

It's the best use of "the wonder" wraps IMO. Although today if you where to apply felt to a McMansion you'd never sell it as perception is stronger than common sense.

But it breathes , they say, once it's dirty it doesn't work that well , and by dirty it can mean it has sawdust on it, residue from the siding on top of it , etc.

But for a under floor bug barrier and to cut down on the wind blowing the insulation out of place etc , it's a good choice. The 1/4" wire mesh I had forgotten about that aspect of the underfloor process , but it sounds like a great idea.

Danfish you have to remember a lot of these cabins are open underneath , no crawl space , so the wrap and wire are a protection barrier that breathes. It won't get much UV exposure , and it's not going to get wet from rain , maybe from flooding , but that's a different kettle of fish if the river near by floods , yer on yer own!!

glenn kangiser · September 05, 2011, 11:48:41 AM

As PEG mentioned - Tyvek or other "Wonder Wraps" are good for the masses who buy the advertising or for covering the underside of a house (or cat box) but good old Felt is superior for prevention of damage to your hard work on the side of your house.

Wonder if they are going to breath out the vapor, or trap the water in the wall cavity through that bad penetration ...

September 05, 2011, 06:38:06 PM

What we are using under the floor joists and insulation..... My DH works for a newspaper and at the print plant they use thin stainless steel plates that are 23" by 35" for each page. they can only use them once then they scrap them. so we will get them for scrap price or less. Hopefully less!

We used them to roof a tool shed and it has never leaked!!. We will probably leave tiny gaps between them when installing for ventilation but not big enough for any rodents to get through.
I know the house we have now we used chicken wire and it hasn't helped much. our cat tears it down.

and it lets spiders in EEK.
as for skirting the sides we haven't decided that yet.

MountainDon · September 05, 2011, 06:58:26 PM

Chicken wires usually has holes that are two large to stop mice. Spaces should be 1/4" or less, 19 gauge welded wire.

NPS Rodent Exclusion Manual links

keyjoy · September 05, 2011, 07:06:58 PM

Quote from: MountainDon on September 05, 2011, 06:58:26 PM
Chicken wires usually has holes that are two large to stop mice. Spaces should be 1/4" or less, 19 gauge welded wire.

NPS Rodent Exclusion Manual links

EXACTLY!! That's why the kitty tears it down

AND that's why we are using the metal plates on the new house.

And we won't leave more than 1/4 inch gap between the plates.

Don_P · September 05, 2011, 07:27:57 PM

Why are we looking at the floor differently than a sheathed wall?

MountainDon · September 05, 2011, 08:30:48 PM

I did ours in 3/8 plywood except for a narrow strip along the inside of each beam. That had the 19 gauge, 1/4" hardware cloth nailed on first (6" wide), then the plywood. The insulation is up against the sub floor and held with spring steel wires "holdem-ups". I did the open strips just to have an exit for water if somehow some got into the joist bays. Maybe I could have done without them. But the plywood has done a good job at excluding rodents, no traces of gnawing or anything.

September 05, 2011, 09:59:49 PM

Ok, after some research I found some examples were liquid water was trapped on the topside of Tyvek when used on bottom side of floor joists. While water vapor will pass through this material, liquid will not. The manufacture does not recommend this use. Gravity drains liquids in the case of vertical installation. Liquids can come from above due to condensation, leaks, etc.

DirtyLittleSecret · September 06, 2011, 08:57:02 PM

Hence the need for "slits" to help it breathe and allow any excess to flow...however, my footings have the cabin about 2.5 ft off the ground. Plenty of ventilation.

considerations · September 16, 2011, 08:49:30 AM

"my footings have the cabin about 2.5 ft off the ground."

Mine's about 4' off the ground...and the Tyvek gets pierced each time it gets fastened....I'm more confident about the longevity of the under floor insulation. The houses I've been under (not a lot) look pretty awful in the crawl space...shredded insulation everywhere.

Alan Gage · September 16, 2011, 09:03:56 AM

Quote from: considerations on September 16, 2011, 08:49:30 AM
"my footings have the cabin about 2.5 ft off the ground."

Mine's about 4' off the ground...and the Tyvek gets pierced each time it gets fastened....

I wouldn't think the perforations where it's stapled in place would do much good for draining water. If water were to get into the floor and on top of the tyvek it would sag down between the joists, leaving any stapling perforations high and dry.

Not saying it's not a good idea to use it, I don't know. Just saying I wouldn't rely on any holes where it attached to the joists to provide drainage.

Alan

considerations · September 16, 2011, 10:23:59 PM

"Not saying it's not a good idea to use it, I don't know."

By next spring the field testing should be complete, and I'll give a full report.