In-floor radiant - how close to the rim joists???

[stee6043]

RE - Staple Up Radiant:

I've seen some conflicting information from different sources on how to layout the pex on the outside edges of your floor. Some folks say to avoid putting any pipe in your last joist bay and stay 12" away from the rim joist at the end of the every joist bay. Other sources say to double up on the piping in these locations.

Any thoughts? My personal preference would be to omit the piping in the last bay and within a foot of the rim joist on the ends of the bays. I don't know why I would want to encourage more heat loss through the rim joist/edge of the floor by doubling the pipe. But at the same time will I notice these cool spots upstairs????

Any thoughts are greatly appreciated...

 

[velvetfoot]

I'm no expert, but the rim joist bays should be insulated and people are saying at least some foam at the end.
It gets pretty cold in that area, and if the system isn't running maybe it could freeze.

 

[in hot water]

no need to go under the wall of course. I like to see at least 6" of spray foam at the rim joist. Foam insulates and really seals any air infiltration better than fiberglass. Or blocks of foam put in place with expanding spray foam.

Where the joists run parallel with the rim, insulate the first joist bay and start radiant tube in the second space in. With 16" OC spacing that puts your first loop in a good spot, not under the walls above or in the rim joist bay.

Where the joist run adjacent to the rim start 6-8" back from the rim, a 8-10 if you have 2X6 walls above.

Some installers will double up the tube in the first bay, really depends on the heat load. I like to add extra in the end space if they have a large loss like big glass on the exterior. Two tubes per joist bay handles most loads up to 25- 27 btu/ sq. ft.

But you really need to do a room by room heat load calc to answer the "how much tube and what spacing" question. Floor coverings have a big effect on radiant. I'm not a fan of radiant under carpet and pad, stick with hard surfaces tile, wood, etc. At LEAST an R-19 under radiant, even if it is over heated space below. No need to warm the ceiling below.

hr

 

[stee6043]

Thanks, Hot Water. That's helpful. I haven't completed my plan for sealing the rim joist yet. I don't want to pay the long dollar for someone to come in and spray foam...but I do plan on putting some thought into it. R30 at the minimum and possibly some added foamboard or something...

 

[in hot water]

www.tigerfoam.com has kits to spray foam yourself. You may find these kits at some of the Box Stores also. I think a few layers of 2" foam sealed in with spray can foam works also.

Often the air leaks are where the rim touched the plate on the wall or foundation, or the plate to foundation connection. That's where the spray foam really seals things up.

Infiltration (air leaks) are a bigger leak for heat than most realize. It's a hard number to calculate without a blower door test on the basement or crawl space. Anywhere you see a spiders web, nearby there is a passage to the outdoors, so the pros tell me.

My plan is to drape InsulTarp, white side up to brighten up the space, in my crawl. Tarp over the gravel base and right up to the bottom plate on the block foundation. Then blocks of foam around the rim with a thin coat of tiger foam to seal it all up.

www.buildingscience.com has excellent info on sealing crawls and basements.

hr

 

[stee6043]

www.tigerfoam.com has kits to spray foam yourself. You may find these kits at some of the Box Stores also. I think a few layers of 2" foam sealed in with spray can foam works also.

Often the air leaks are where the rim touched the plate on the wall or foundation, or the plate to foundation connection. That's where the spray foam really seals things up.

Infiltration (air leaks) are a bigger leak for heat than most realize. It's a hard number to calculate without a blower door test on the basement or crawl space. Anywhere you see a spiders web, nearby there is a passage to the outdoors, so the pros tell me.

My plan is to drape InsulTarp, white side up to brighten up the space, in my crawl. Tarp over the gravel base and right up to the bottom plate on the block foundation. Then blocks of foam around the rim with a thin coat of tiger foam to seal it all up.

www.buildingscience.com has excellent info on sealing crawls and basements.

hr

Ughh....that stuff is so pricey. I can run R19 under my entire floor for nearly the same cost as the smallest amount of spray foam. I'm inclined to buy a roll or two of the highest R value fiberglass I can get and run a 12" perimeter with that. The cost would be a fraction....why must money always get in the way???

 

[RobC]

re: foam insulation. I foamed my roof cavity (catherdal cielings) 5 or 6 years ago and have been very happy. It's a sound dampener, has added rigidity to the building structure and is a superb insulator. However the biggest factor gets over looked when comparing R values. Foam products do not cold or heat "soak". When researching foaming my roof I came across a comparison of insulation types. My recolection was that in prolonged cold or hot events, lets say 2, 3 or 4 days or longer foam highly out preforms batt insulation.
I also found a big difference ( try 50% ) in pricing with the same product but with different installers.

This is from a vendor's web site that I just found:

Heat loss occurs by Conduction, and Convection. Conduction is the transfer of heat through solid molecules, this method of heat transfer is the slowest. Convection is the transfer of heat by liquid or gas molecules moving from hot areas to cold areas. This results in a convection current transferring heat energy from warm areas to cold areas, this method of heat transfer is the fastest.

Stopping Convection stops heat loss. 80% of heat loss in a building is due to convection, with only 20% of heat loss due to conduction. Most insulation methods address convection, albeit in different ways, and with different results.

Fiber Insulations slow convection, Foam stops convection. Fiber Insulations like Fiberglass, Cellulose, and Rockwool are designed to slow down air molecules, and as such they can only slow down convection. However as the exterior temperature drops, convection currents speed up and Fiber Insulations become less and less effective at slowing these convection currents down. As a result heat loss increases. Foam is designed to stop convection by stopping air infiltration.

 

[Chris S]

Hot Rod is correct. Sealing the air leaks is the most important part of your installation. You can stuff fiberglass in the beam ends all day and run tube after tube of caulk, and canned foam ( I have a Hilti dispenser- much better than great stuff) and it will not compare with a sprayed foam job covering the sill plate and lapping onto the foundation. If you have any air movement, you will not realize the heat in the room above, and air does move easily through fiberglass. Foam- not so much.

What Hot rod is describing with board foam & spray foam is also effective, but very time consuming, and not a lot of people ( Hearthdotcom dwellers aside) would have the patience & ability to install well enough for it to be viable.... And it does not address the sill plate to foundation joint which is potentially a big heat loss area. In my new installations, we insist on sprayed foam beam ends up and down if 2 story, even if there is no radiant involved. This is kind of like the extruded plates vs: aluminum flashing argument. Do it once & do it right, it will pay you back for years to come.

 

[pybyr]

re: foam insulation. I foamed my roof cavity (catherdal cielings) 5 or 6 years ago and have been very happy. It's a sound dampener, has added rigidity to the building structure and is a superb insulator. However the biggest factor gets over looked when comparing R values. Foam products do not cold or heat "soak". When researching foaming my roof I came across a comparison of insulation types. My recolection was that in prolonged cold or hot events, lets say 2, 3 or 4 days or longer foam highly out preforms batt insulation.
I also found a big difference ( try 50% ) in pricing with the same product but with different installers.

This is from a vendor's web site that I just found:

Heat loss occurs by Conduction, and Convection. Conduction is the transfer of heat through solid molecules, this method of heat transfer is the slowest. Convection is the transfer of heat by liquid or gas molecules moving from hot areas to cold areas. This results in a convection current transferring heat energy from warm areas to cold areas, this method of heat transfer is the fastest.

Stopping Convection stops heat loss. 80% of heat loss in a building is due to convection, with only 20% of heat loss due to conduction. Most insulation methods address convection, albeit in different ways, and with different results.

Fiber Insulations slow convection, Foam stops convection. Fiber Insulations like Fiberglass, Cellulose, and Rockwool are designed to slow down air molecules, and as such they can only slow down convection. However as the exterior temperature drops, convection currents speed up and Fiber Insulations become less and less effective at slowing these convection currents down. As a result heat loss increases. Foam is designed to stop convection by stopping air infiltration.

Fiberglass insulation does indeed have issues with convection within the insulation, as well as air leakage through it (If you take apart a wall with fiberglass insulation in it, you can often observe some areas that are particularly dark and dirty near areas that air is leaking through (electrical outlets, cracks between siding and sheathing, etc)-- the fibers act as a 'filter' of sorts-- indicating that air (carrying warmth) is moving through. Plus, in any situation in which it's not entirely enclosed, rodents seem to delight in nesting in it and/ or carrying off the fibers.

Dense-packed cellulose is substantial enough to have little air convection in it, and lets little air through it. It'd be hard to install in Stee's situation around a band joist/ perimeter-- but then again, there is some stuff known as "damp spray" cellulose, in which the material has a small amount of moisture added during the application (and- I'm told- sometimes, but now always, a bit of Elmer's glue)-- with the moisture causing it to adhere to a surface and stick together. Perhaps check with a local cellulose insulation contractor.

PS, I'll second Hot Rod's point that "Infiltration (air leaks) are a bigger leak for heat than most realize."-- finding and sealing air leaks in the lower and upper parts of a house can make a vast difference- sometimes with surprisingly little cost and difficulty-- and if you put up fiberglass around the sill/ band joist without checking for leaks first, then the air is still going to leak through.

 

[Jackpine Savage]

I removed the fiberglass insulation from my rim joists last winter. I was amazed at the drafts (breeze) that came through. I went the foam board/spray foam route. I put in the foam boards and left 1/4" gap all around and then filled the gap with spray foam.

 

[velvetfoot]

When I removed the fiberglass from the rim joist area this winter to replace it with foam boards there was frost on a good number of them.
It condensed vaper that passes through the fiberglass.

All that cutting and fitting in a crawl space doesn't sound too appealing. Maybe an estimate from a pro foamer?

 

[pybyr]

For anyone who's going to be doing any significant amount of DIY foam insulation (such as air sealing, filling voids around foamboard, etc) you definitely want to get a _real_ foam gun, not just the use& toss cans. The 'pro' foam applicators are far easier to use, allow you to use part of a can and keep the rest for later, and the $ per unit volume of foam is less. Here's what I got, and where I got it from:

(broken link removed)

 

[SolarAndWood]

Is $12/cu ft the best you can do for any of the DIY foam kits? How much does it cost to get into the 55 gallon drum game? How much less is the material cost then?

 

[rfactor]

For insulation against the rim joist I used foil-bubble-foil against the rim joist, caulked the edges and then put 4" of cotton bat insulation. I put the tubing probably 8" from the rim which may be too close according to some.

I no longer use fiberglass insulation. It seems to decompose over time, rodents love it and is horrible to work with.

Rurik