Sooooo…… here’s the situation: I am installing 3/4″ T&G maple flooring. Upstairs radiant floor construction is TJI’s covered in 3/4 plywood with 2×4 sleepers on 18″ centers. Radiant floor tubing zig-zaged in between the sleepers and covered in 1 1/2″ Gypcrete. The mason has installed slate flooring in some areas, holding the finished level 3/4″ above the sleepers, allowing for the wood floor to meet the stone edge flush.
Here’s my question: Should I nail the maple flooring directly to the sleepers, or put down a barrier of some sort first?
IslandJim
Replies
IslandJim
The reason a barrier is used is often the concrete is in direct contact with the ground and wicks up moisture. Since that is not the case all a vapor barrier will do in your case is slow transfer of heat into the floor (make the system less effective)
Another words no vapor barrier required.
Thanks Frenchy. Agreed. No moisture transfer possibilities here. It's an upstairs floor.
My concern is that some installation techniques call for a layer or two of plywood sub floor installed between the sleepers and the maple, presumably to help dissipate the heat transfer from the radiant tubing to the maple. My worry is that the maple may be too close to the heat source and shrinking and swelling of the finished maple may occur. Therefore some thin membrane may help even the heating out. Or maybe that would just inhibit the heating and make it less efficient? Anybody with any experience with this sort of installation?
From a heat transfer standpoint a thin membrane will have little if any measurable effect. It depends on the heat transfer capability of the membrane, but it is so small of a mass in comparison to the gypcrete bed, and the flooring that it won't have much effect. If your feeling rich, you could put in some 0.020 aluminum shim stock and it might make a difference.
The two layers of plywood would definitely change the thermal mass enough to effect the heat transfer, but you don't have the room for them vertically.
You might look into some of the higher end engineered wood flooring. Being a high grade plywood, with a maple top surface, they are more resistant to movement due to moisture changes. Being thinner you would have to put in a layer of plywood to get your heights to match. But I don't think it would change the thermal cycle, it would just make the top surface less susceptible to moisture caused shrinking and swelling.
If you are really worried about it, check the Forest Products Lab website for the information on dimensional changes in maple due to moisture, and compute what it will be for the width of planks you intend to use.
IslandJim
Wood doesn't shrink or swell from heat.. (metal does, wood swells or shrinks from moisture) *note; it shrinks and swells in width not in length.
There is a slight R value to wood so the thicker the wood between your feet and the heat source the worse the transfer of heat will be.. I like rosin paper simply to allow the wood to move slightly as it swells and shrink as moisture varies.
That thin layer of paper will do nothing to spread the heat or isolate the maple from it. What you have is less than an ideal situation any way you look at it. Nailing at 24" OC for strip flooring over gyp is what would bother me the most. That is just not close enough to hold anytime, but with the heat yanking on the flooring, it will be worse.The way to control the damaging effects of the heat under a wood floor is not only with subfloor layering, but tempering the heat delivery at the mixing valves. You can have it up to something like 111°F to 114° for masonry, but for wood floors nothing over 98°F delivery, IMO.Are you the installer as a sub or are you the owner?
This sounds poorly planed in the design phase to me. edit - I just re-read the OP and see it is 18" OC. That is better, but still bothers me some. I like nailing at 8-12" depending on the floor. 18" minus 3-1/2" leaves 14-1/2" free of fastening over the gypcrete. Have you got a lot of longs or typical maple with shorts all the way down to 8"?
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Edited 7/29/2008 9:13 pm ET by Piffin
I am the installer, not the owner....so I wasn't part of the planning process, nor did I get a voice in choosing the flooring material. I just get to be the installer/finisher guy.
The maple has some good lengths to work with.
Jim
Be very careful and very scared. You are the one they will blame. I don't know if a disclaimer will help.
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Do you think slapping a coat or two of finish to the underside would help any?
Not much.I thought of gluing it down too, but don't know how well that works for gypcreteBest thought here was the thinner engioneered flooring so he could run some ply over the sleepers, but he already had the material on site.I'd want it pretty dry
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Maybe PL premium down the center of each board? Be something to ask PL or http://www.awc.org/index.html
before going to the extra trouble.
Bostic makes a good woodflooring adhesive I have used for similar on crete. It has some slight movement whereas PL Premium cures and locks up tight.
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Piffin
You claim that you are experienced and yet you perpetrate it the idea
that heat affects wood?
Shame on you (or in Piffin speak, you're lying) heat does not affect wood moisture does and you should darn well know it!
I don't know what you are having a hissy fit over.Heat directly under a wood floor drives the moisture out of it and causes it to shrink excessively and sometimes unevenly, making it yank according to what sort of grain and milling it has.The temps I mentioned are in the install book of basics for the radiant heat people and they are at those limits because of experience and testing. There bypassed the kooky thoughts of a northwoods equipment salesman cum DIY HO builder.
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piffin,
Just trying to follow your example of attacking every single word you post.. But you have to agree heat doesn't shrink or swell wood..
You're just doing the same thing you accuse me of doing.
I absolutely agree that heat does not shrink or swell wood, but that was never the concern here.As for the other, that is your personal problem.
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This is from http://www.simplysuperbfloors.com/faq.html
It does not clear up your question part 1 says to use a vapor retarder no matter where a slab is. One can argue gypcrete is not a slab. Part three referring to gypcrete does not make reference to a vapor retarder. But the last paragraph says not to use felt or rosin paper.
I would go with using a 6 mil polyethylene over the gypcrete, the crete does absorb moisture, maybe not in heating season but in the seasons the system is off.
Wallyo
Can radiant heating systems be compatible with wood flooring both solid and engineered?
"YES" with certain cautions and restraints.
First of all, check with the manufacturer for their recommendations.
The most common recommendation for all systems is to have the heating system installed and "on line", running, before wood flooring products are delivered. Most contractors report a minimum of 72 hours of heating is required to dry the system; however, a week or more is suggested. Light weight concrete, gypcrete, gypsum slurrys, etc. tend to dry slowly so that the extra time is necessary.
For engineered flooring: adhesive applications, the adhesive manufacturer should be consulted for compatibility with the heating system. Engineered flooring mechanically fastened, - use fasteners which do not extend below the subfloor material.
For solid wood flooring, the following three installation systems are the most common:
1) Plywood subflooring over the heated slab. If the slab is on grade, above grade, in contact with the ground, or over an uncontrolled environment; a vapor retarder of 6 mil polyethylene, should be placed over the slab. Do not glue the polyethylene. A proper subfloor can be composed of 2 layers of 1/2" plywood, southern yellow pine or douglas fir. The first layer is placed on the normal square of the room; the second layer on a 45 degree angle to the first layer; space 1/4" to 1/2" around the perimeter of panels of both layers; pin plywood together with 7/8" ring shank nails or screws; nail from center out on a 6" grid pattern, avoid trapping a hump between layers; nail flooring to plywood with fasteners which do not extend below plywood. You may have to cut the nails for face nailing starter and finish runs. An alternate method is to use 16" wide x 8' long 3/4" thick plywood planks, scored across the back 3/8" deep every 12" or so. Score more often if curling of the plywood is a problem. Lay these planks over the slab perpendicular to the direction of the flooring and stagger plank ends at least 2 ft. with up to 1" space along edges and 1/8" to 1/4" space between ends. Always use at least a 2 ft. length of plywood plank at flooring starting wall and ending wall. Fill in short pieces in the center of the room. Again use appropriate length fasteners (1 1/2") for blind nailing and cut the nails to less than 1 1/2" lengths for face nailing.
2) Conventional wood joist construction with heating tubes fastened to the underside of the subfloor; with this installation fastener length is important also. No fastener should penetrate through the subfloor and risk puncturing a tube.
3) Conventional wood joist construction with 3/4" or thicker firring strips fastened to subflooring; the heating tubes run between the strips with light weight concrete, gypsum, etc., poured over and around the tubes filling the space between the firring strips. The flooring is nailed to the firring strips. Firring strips should be group #1 dense softwoods (southern yellow pine, douglas fir, larch, etc.) spaced 12" on center or less and well attached to the subfloor. Flooring is oriented perpendicular to firring and nailed to firring strips.
When deciding on radiant heat under hardwood flooring keep in mind the following:
1) Strip or plank less than 4" wide is recommended, the more narrow the better . Edge grain or quartered product is also more stable.
2) Use a moisture meter to check average moisture content of the flooring, make 20 or more readings and average them.
3) Acclimate to the average condition of the area. Heating does not occur year round so the contractor must allow for the expected flooring expansion of the non-heating season, in most areas. In other words, try to avoid installing a very dry flooring product over a very dry system in the winter with the heat running. If flooring has to be installed under these conditions provide adequate field expansion or "spacer rows" to accommodate expected expansion.
4) With radiant floor heating some extra cracks between strips may be expected in the finished floor during the heating season. But they should not be significantly greater than a non-heated floor where proper installation guidelines are followed and occupied jobsite conditions are met.
5) Provide an outside thermostat to call for heat during rapid outside temperature drops. These heating systems are slow to react and pre-heating helps even the demand load. Do not use "set back" thermostats. Continually changing the temperature shocks the flooring and finish with excessive heat and can cause performance problems.
6) It is not necessary to use asphalt felt (or rosin paper) under flooring as some odors may develop when heated.
In summary, wood flooring and radiant heating can perform very well together for the life of the structure. Be sure the job site is ready for the flooring installation and check the moisture content of the flooring to establish the present condition and provide necessary spacing for the expected movement.
Edited 7/29/2008 11:22 am ET by wallyo
How recently was the gyp installed and what is the MC?
How recently was the gyp installed and what is the MC?
The Gypcrete has been down for several months. The 3/4" thick x 2 1/2 & 3 1/2 width maple flooring bundles have been acclimating in the house for several months.