We are in the process of purchasing a home constructed of post and beams. The crawlspace is used as a plenum for a geothermal heating unit. Does anyone know if a post and beam constructed house has to have a plenum to keep it from having structural damage to the posts?
This house also has tested postive for radon gas. Is there a way to mitigate a plenum without losing all of the heat?
Thank you!
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Replies
Lizabee:
I'm afraid I don't really understand your question. Are you saying that the crawlspace is being used as one giant return or supply duct for your HVAC system? What do you mean by mitigate? Do you want to find a different way to handle the supply/return air to reduce the Radon infiltration and are you concerned that this change of method will effect the P&B frame?
BILL
Yes! We would like to change the HVAC system to a gas and put vents into the crawlspace. We are worried that with post and beam construction that the HVAC system is there because of the type of construction.
How stable is Post and beam construction? We are thinking of purchasing a home and it is scaring us away because of the type of wood foundation. Plus testing postive for radon gas. It needs to be vented (mitigated) so the gas will not be coming into the house. With the vents being a plenum, the gas just comes in. We wanted to vent that crawlspace and put in vents for the heating system.
Hope this makes better sense. Thanks! LIzabee
lizabee:
Post & Beam is a type of Frame not a type of foundation. If this house does indeed have a wooden foundation, you would be well served to have a qualified home inspector or an engineer take a look at the place. Get an independent opinion, not someone recomended by the realtor. Go to the National Association of Home Inspectors web site or look under engineers in the yellow pages. Try to find someone who has experience with wood foundations as they are not very common.
The biggest drawback to a wooden foundation is that unlike concrete or block, they hava a lifespan (30 years plus?) based on the soil conditions, and the quality of the original work. No one can assess those factors or the condition of the foundation without taking a close look at it.
Good Luck
BILL
Well, sometimes and some places, the term "post and beam" is used to refer to the post and girter structure within the perimeter of a stemwall foundation, or a building supported on a system of posts and beams serving as the foundation support for the building.
But I'm still a little unclear about what lizabee is describing. The homes I've seen with an enclosed, insulated crawlspace acting as the plenum, don't sport "vents."
If the crawlspace area is indeed the plenum, there should be no threat to the "post and beam", because it is located in a dry, heated space.
Notchman:
Absolutely correct, "My Bad". If the structural members are in the conditioned space they are well protected but it sounds to me like there is something strange going on here that we're not able to see.
BILL
I think you should determine the status of the radon gas and where it is coming from. Based on your message, I assume it is coming from the crawlspace.
I would need more information to understand what is going on with this house. (Wood foundation? Geothermal heating - what is the process of heat transfer used?) It is very unusual to use a crawlspace as a heating plenum. Where are you located? What is your annual temperature range? How is the perimeter of the crawlspace insulated? Usually you would find sheet metal supply ducts in the crawlspace, ducted to perimeter floor heating outlets. The crawlspace usually requires venting to prevent accumulation of moisture, though these are often closed during the cold winter months (I leave mine open).
You definitely don't want to touch a home (project?) such as this without expert advise in the form of a home inspection by someone knowledgeable about the heating system, the foundation and the radon gas problem (that one would do it for me - I'd be walking).
From a retired heating (HVAC) engineer.
Brian