Insulating my old back house floor?

1910NE · 09-30-2010, 12:43 AM

Hey folks,

The back house on my 1910 New Englander (Southern Maine) is an old shed which sits 24" off the ground on a few (too few) concrete piers. I need to insulate underneath before winter arrives, because this building has a bathroom and laundry room in it. When I bought the house, the plumbing supply lines all ran under the structure, and had burst from freezing, including the hot water heating system. I have replaced the plumbing with PEX, and it is now all within the insulated envelope, and the rooms are will now be heated with 220 electric heaters. However, I want to insulate the floor so that the rooms are not freezing cold this winter.

I plan to do the following...
1) Install bat insulation between the floor joists ( 24" OC x 8" depth.)
2) 1/2" Ridged over the bats to help keep it in place, and to keep the critters out.
3) An insulated box around the tub trap, which sticks down below the floor joists. I also have the ability to drop a piece of heat tape into this box from inside the building if necessary.
4) Vapor barrier on the bare dirt under the building
5) Insulated, pressure treated skirt around the perimeter, to keep the wind from howling through underneath.

I should add that I intend to demo this structure within a year or two. If I did not need the bathroom and Laundry, I would probably just winterize the plumbing and not worry about it. Any suggestions? Holes in my plan? Am I overly concerned?

Thanks in advance!

wombosi · 09-30-2010, 09:48 AM

interesting conundrum.
i have a similar addition at my place built on piers and it's taken me a long time to come to terms with keeping it rather than razing it.

if you're tearing it down in a year or two, i personally wouldn't put a penny into it. maybe staple up some poly across the bottom of the joists to help with air infiltration or something. but basically i would suffer through a winter or two of inefficiency unless you think that the insulation efforts would be significantly cheaper than the compensated heat cost.
i would just box in the trap with ridgid and spray foam and/or heat tape, and on really cold nights you can drop in some salt. it's said to prevent freezing.

on the other hand, if you decide to keep the structure, your plan sounds decent. personally i would spring for blown-in expanding foam in the floor cavity, and forget about insulating the skirting walls and vapor barrier on the floor.

i would skirt the walls with PT and stucco over it.

good luck.

rjniles · 09-30-2010, 10:34 AM

Since you are going to the building, I second on spending as little $$ as possible. Do what I have seen many times in Maine and my father did in a rental after he moved to Connecticut. Staple up tar paper (asphalt builders felt) around the perimeter and rake up bags of leaves to stack around the foundation. Or use bales of hay.

1910NE · 09-30-2010, 04:36 PM

Thanks for the input everyone. Unfortunately, keeping this structure is not an option. It is visibly falling away from the rest of the house, the gabled end wall bulges out almost 6 inches half way up (due to a former owner cutting some rafters indiscriminately,) and the sills are all rotten. To date, I have not been able to determine if there is anything besides gravity holding it to the rest of the house. The only reason it is still standing (thanks to some new foundation piers) is that it has the one working bathroom in the place.

Its not an ideal situation, but I have been forced to throw some time and effort at the darn thing, even though its days are numbered. I have designed a replacement structure which will keep the farmhouse feel, and provide a much better use of the space. I will spend the winter finalizing the plan, working on permits, and lining up the parts that I plan to contract out. Hope to post pictures of the demo some time late next spring.

until then, I need to keep it warm.

eastside · 09-30-2010, 08:09 PM

Your situation describes mine. Same thing. Contractors looked, shook their head and said tear it down. Walls bowed out, rafters sagging at least 6 inches (water damage) sill plates rotted, the floor was bad, several floor joists rotted right away.

I rebuilt the entire thing from the inside out. I"m not a contractor but I amazed myself and had a lot of rewarding challenges.