Tag Archives: radiant floor heat

Slab on Grade or Crawl Space?

Slab on Grade or Crawlspace?

Long-time readers of this column recall seeing a profuse number of articles written in regards to crawl spaces. These articles have been on a gradual increase since this first one six years ago: https://www.hansenpolebuildings.com/2013/03/crawl-space/.

With residential post frame construction becoming rapidly more popular as more people discover this system’s benefits, this debate of slab on grade versus crawl space will continue.

Hansen Pole Buildings’ Senior Designer Wayde recently had a client order a new post frame building kit package with an elevated wood floor (to create a crawl space). After client has placed their building order, Wayde came back to me with this, “Can you tell me the Pros and cons of building this as we designed and sold it vs. lowering it three feet and adding a radiant concrete floor?”

I happen to be a big fan of hydronic radiant floor heat in concrete slabs, we have it in our own building: https://www.hansenpolebuildings.com/2012/08/radiant-floor-heating/.

Biggest pro of “as is” – living upon a wood floor will be so much more comfortable than upon concrete. Wayde’s client could still do radiant floor heat, should they opt to not go with a forced air HVAC system.

Slab on grade the client will have to (or should) do a post frame shallow frost protected foundation: https://www.hansenpolebuildings.com/2019/02/minimizing-excavation-in-post-frame-buildings/. This perimeter rigid board insulation must be covered with rodent proof material.

If I went to slab on grade, I would recommend a minimum R-60 for ceiling, taking a 22 inch deep raised heel truss to allow for adequate depths of blown in insulation. (Read more about raised heel trusses here: https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/).

For an 8′ finished ceiling, they would then need an eave height of 10′ 4-5/8″. I like taller rooms, so you might want to experiment with eave heights of 11′ 4-5/8″ and 12’4-5/8″ (latter of these will be easier to drywall and will result in least waste).

Making a choice between living on concrete or wood will be one only able to be made prior to time of construction and should not be taken lightly. All factors should be taken into consideration most importantly being what creates a most comfortable living space.

PEX Tubing

I’ve espoused previously on the joys of hydronic radiant floor heating (https://www.hansenpolebuildings.com/2012/08/radiant-floor-heating/) and would encourage anyone who is going to install a concrete slab on grade in their new (or existing) post frame (pole) building to consider at least making a provision for it in the future.

As we all realize, once a concrete floor is poured, it is literally “cast in stone”. Without huge expenses, there really is no going back for a do over.

pex tubingThe key to being prepared for the future, is to have PEX tubing installed in the concrete slab at time of pour.

PEX (or crosslinked polyethylene) is part of a water supply piping system which has several advantages over metal pipe (copper, iron, lead) or rigid plastic pipe (PVC, CPVC, ABS) systems. It is flexible, resistant to scale and chlorine, doesn’t corrode or develop pinholes, is faster to install than metal or rigid plastic, and has fewer connections and fittings.

PEX tubing is made from crosslinked HDPE (high density polyethylene) polymer. The HDPE is melted and continuously extruded into tube. The crosslinking of the HDPE is accomplished in one of three different methods.

Crosslinking is a chemical reaction which occurs between polyethylene polymer chains. Crosslinking causes the HDPE to become stronger and resistant to cold temperature cracking or brittleness on impact while retaining its flexibility. The three methods of crosslinking HDPE are the Engels method (PEX-a), the Silane Method (PEX-b), and the Radiation method (PEX-c). Several industry participants claim the PEX-a method yields more flexible tubing than the other methods. All three types of PEX tubing meet the ASTM, NSF and CSA standards.

Some applications require PEX with added oxygen barrier properties. Radiant floor heating (or hydronic heating systems) may include some ferrous (iron-containing) components which will corrode over time if exposed to oxygen. Since standard PEX tubing allows some oxygen to penetrate through the tube walls, various “Oxygen Barrier PEX” tubing has been designed to prevent diffusion of oxygen into these systems. Two types of specialty PEX pipe are offered:

Oxygen barrier PEX has a layer of polymer laminated to the outside surface (or sandwiched internally between PEX layers) which prevents oxygen from penetrating. The polymer film is usually EVOH (ethyl vinyl alcohol copolymer), used in the food industry as an oxygen barrier.

PEX-Al-PEX (or PEX-Aluminum-PEX or “PAP”) is a specialty PEX tubing manufactured by several suppliers. This tubing has a layer of aluminum embedded between layers of PEX to provide an oxygen barrier. PEX-Al-PEX may also be called multilayer pipe or composite plastic aluminum pipe. PEX-Al-PEX will also retain shape when bent, and may also exhibit less expansion and shrinkage during temperature fluctuations, but may be less flexible than PEX tubing. PEX-AL-PEX costs about 30% more than standard PEX.

As with so many things construction, there is one opportunity to do something right or wrong, personally I would recommend making the extra investment in PEX-Al-PEX. The few extra dollars can lead to a lifetime of happy heating for your new pole building.