Replies

1. 
   Piffin | Oct 28, 2002 02:28am | #1

   The Homasote that I'm familiar with would still need plywood under it fro support. It has no strength to speak of. Long ago and far away, we used to put it over the plywood for a layer of insulation. Maybe the company puts out an itegral product now that does both together

   .

   Excellence is its own reward!

1. 
   jesup | Aug 19, 2021 09:16pm | #10

   Replying to an ancient message - but Piffin likely is thinking of Homasote 440 insulating boards (1/2" thick); Homasote roof decking ("Easy-Ply") is ~5 layers of the same panels, bonded together, tongue-in-groove edges, and faced on one side with vinyl. The roof decking can span 4' OC and is very stiff; R5

2. 
   xMikeSmith | Oct 28, 2002 03:19am | #2

   the insulation value is nil.... about 1.. vs. maybe .5 for plywood... as a nail base it has very little holding power.

   if it gets wet it will stay wet longer..

   what you really seem to be asking is would you use it as a nail base to go  over the skip sheathing... no.. i'd use either 3/8   or 1/2 plywood

   Mike Smith   Rhode Island : Design / Build / Repair / Restore

1. 
   Piffin | Oct 28, 2002 12:38pm | #3

   Actually, I researched their site.

   http://www.homasote.com/ep.html

   They've got a couple products, one is thermasote with R value up to 5 and another roof decking material with a fiinished vinyl surface.

   I'd want to see samples before planning to use it though.

   Excellence is its own reward!

1. 
   xMikeSmith | Oct 28, 2002 02:18pm | #4

   yes.. i've used thermasote.. but he said homasote.. ( generic..like kleenex ?).. and don't you think he'd still better off with cdx ply as a nailbase ?Mike Smith   Rhode Island : Design / Build / Repair / Restore

1. 
   Piffin | Oct 28, 2002 11:27pm | #6

   Definitely, which is why I said tyhat I'd want to see it before using it - the other product they have that is- to see if ply was a part of its structure. That's implied but not 100% clear online..

   Excellence is its own reward!

3. 
   Mongo | Oct 28, 2002 08:00pm | #5

   Geoff,

   "Homasote?" No, don't use "homasote". Not as you've described.

   How about another product from the "Homsasote product line?" Possibly...but first a couple of assumptions on my part. One, "the rafters are 2 x 4." Assuming these are not trusses, then I'll venture that you have an older house...maybe a bungalow or cottage. Even if I'm wrong there, I'll drone on...

   "Structural" homasote does not like water, regardless of thge state of the water...solid, liquid, or vapor. In most roofing systems, water vapor will most likely to cause damage with homasote, in that homasote is recycled cellulose. It will absorb water vapor, and the absorption process will reduce its stiffness and cause it to sag. You don't want that in a roof system.

   In general...and by that, I mean...in general...homasote products are not specified in residential roofing construction unless the installer knows what he is doing, the crew is detail-oriented, and the entire buiding envelope has been well-built in regards to addressing water vapor in the envelope. A poorly executed installation may result in failure of the product and may require an early replacement of your roofing system. Even the best installation in an inadequate envelope can cause heartache down the road. In commercial construction, homasote is more common as most roofs are hot and not vented.

   For the best decking as a residential nail base, consider CDX.

   If you need to maximize insulative value in a small rafter space, think of polyisocyanate at R7.2 per inch. Two-inch sheets either ripped and friction-fit or foamed between the rafters from underneath, or full sheets face-nailed to the bottoms of the rafters, then strapping, then gypsum board.

   I use a fair amount of product from the homasote line. I like their products. Still, you need to be judicious in its application.

   Edited: to add "roofing" in previous paragraph.

    

   
   

   ---

   Edited 10/28/2002 9:02:25 PM ET by Mongo

1. 
   geoffmurray | Oct 29, 2002 03:48am | #7

   Thanks fellas,

   I kinda thought the same things you all mentioned. I've used homasote as a sound barrier in double walls. It didn't seem like material that I would put on a roof. But given the product info., it seemed like magic stuff. Insulate and substrate all in one.

   I live in southern BC., pretty wet. Too wet for something like this.

   My plan is to put a room up in the attic of my 1940's, 950 sq ft. cottage style home. I can insulate the rafter space (not trusses) with batt fiberglass, vapour barrier with 10 mil poly, fasten 1 1/2 extruded polystyrene on top of the skip sheathing and sheet over that with CDX.

   Do I have to worry about ventilation in a system like this? Will the skip sheathing provide this?

   thanks

1. 
   caseyr | Oct 29, 2002 05:27am | #8

   My house in El Sobrante, CA (just a little north of Berkeley) has Homasote panels for the roof on 4x4s at 4' centers.  These panels are about 2'x8' and 3" thick.  They are tongue and grooved and slid together and nailed or screwed to the beams.  The roof was then covered with hot mopped tar to provide weather protection. 

   The stuff is pretty easy to work with, I could handle the panels single handed and used 4" deck screws to fasten them down.  The problem is that if the tar and gravel roof leaks, the Homasote doesn't last long and getting a new panel in place can sometimes be a challenge to put in a tongue and grooved panel in the middle of a roof without removing all the panels below it.  My house was built in 1957 and I noticed that several small sections of panels had been pieced in over areas that were not exposed below.

   From below, the ceiling looks like vinyl accoustic panels - perhaps not the greatest but not too bad.  I can't remember the actual R rating of the panels but the comment above of 5 might be right, but I vaguely remember that it was supposed to be 7.  Anyway, I had 2" panels insulation installed on top of the roof when I had the tar and gravel roof installed.

   I can't remember the price of the panels but they were more than I had expected, I think maybe it was around $125 per panel.  They were not readily available but the roofing supply place in Oakland, CA, said they sell a lot of it.  I would guess that it would only be popular in fairly mild weather areas.  The stuff seemed surprisingly strong, the top half of a 60' pine tree fell on my house and the limbs poked a couple of holes in the panels up to a foot in diameter, but it did surprisingly little damage for a goodsize log to blow down from about 15' above the roof and hit it square.  I could jump up and down in the stuff between the 4' centers and not feel it flex particularly. 

   If I were reroof the entire house, however, I would probably consider Structural Insulated Panels before I would think about the Homasote panels, although they might be a little harder to move into position.     

2. 
   Piffin | Oct 29, 2002 01:25pm | #9

   If your poly vapor bar is to the inside of the insulation so moisture is stopped before it gets to the insulation, you wouldn't have to have vents but you have to make absolutely sure to seal all penetrations.

   Excellence is its own reward!