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Log cabin floor retrofit

shawncal's picture

Hi all,

I am moving a century-old Finnish square log cabin to our property this summer.  It is a 1.5 story, 15' X 15' building, with 5" thick timber walls.  It will be used as a cottage year round in Northern Mn, so I would like to insulate the floor and ceiling reasonably well when we reconstruct it.  Currently, it has no floor or roof, so am starting with a clean slate.

The plan is to set the building on a skid foundation of PT 6x6s (probably 2 courses high) on a rubble trench perimeter.  I would like to keep the ceiling vaulted, with some t&g showing from the inside.

I lam curious how best to finish the floor and ceiling to get R-value, thermal breaks, and keep the critters on the outside all year.  

Any thoughts appreciated!

Shawn

I think you've got your work (post #207365, reply #1 of 7)

I think you've got your work cut out for you.

Probably a more detailed description is needed.

In particular, what is the roof structure like, and how do you expect to support the floor?


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Budget (post #207365, reply #3 of 7)

Attached are two pics of the structure.  It has already been dismantled, moved and reassembled once (as shown).  I am purchasing the building as the first buyer decided not to use it.  We will be dismantling and moving it a second time this spring.

This building will be a year round residence, pioneer-style (no running water or power, at least for now).  Good times.

I would love to put it on an ICF basement, or insulated slab foundation, but the budget will not allow it.  So the goal is to make it as durable and efficient as possible on a very limited budget.  I know this does not fit the FH mentality, but it is what it is.

my current thought on the foundation is to put two courses of PT 6x6 timbers on a rubble trench perimeter to act as the sill, then erect the log structure on top of this.  The floor joists would be supported by joist hangers/ledgers attached to the timbers, and so could be built either before or after the walls go up.  If this is an appropriate method, then my next question is how to insulate and critter-proof the floor?  

As for the roof, it is a clean slate.  The building comes with the original pine pole 'rafters' which are covered with tin just to keep the building relatively dry.  I will need to give it a better roof, for insulation and weatherproofness.

Thoughts?

Shawn

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It's important to keep it dry (post #207365, reply #4 of 7)

It's important to keep it dry and well-drained.  The wide overhang of the roof is an important part of that, and how you do the "foundation" is another important part.

Might help to tell us where this is, weather-wise.  (Oops!!  I see --- Northern MN.  Someone's gonna freeze their arse off.)

To preserve the structure, on the "foundation" you propose, requires that it be reasonably well ventillated below the floor.  Which would imply that you will want a airtight and well-insulated floor.

You will need to chink the building well (and consider what you use for chinking), to make it reasonably airtight.

For the roof, unless you're married to the existing poles, I think I'd go high-tech -- some sort of foam sandwich.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Why no conrete and foam? (post #207365, reply #2 of 7)

Why no concrete and foam?

log walls leak... (post #207365, reply #5 of 7)

No matter what method you use for the floor and roof you can expect a heap of air infiltration through log walls.

Probably you don't wish to cover them up inside or out so brace yourself for drafts.

.

Tin Roof (post #207365, reply #6 of 7)

Hi there,

You stated, "...the original pine pole 'rafters' which are covered with tin just to keep the building relatively dry.  I will need to give it a better roof, for insulation and weatherproofness."

Wondering - if, by "better roof", you mean to roof with something other then metal?

Certainly, the original tin may need replacement, but imo metal is far better than say, asphalt shingles.  Better looking, longer
 lasting, at least as [if not more] weather-proofing, and can be insulated.

Just my $.01.

Insulation for the Cabin (post #207365, reply #7 of 7)

Hi- I have 10 years of experience in on a hundred-year-old post and beam barn in MA, as an owner, not that handy as a workman, yet.

Going cheaply, you can't afford SIPS (Structural Insulated [sandwich] panels for roof).  For a 30x40 footprint[mine] $50K!!  Neither can you afford integrated metal panel roofing which would properly expand with the temps and last a long time [$25K!!].  Tin roofing expands and widens the connector holes until they leak, it'll work initially but it is noisy and then leaks, is meant for a car garaage but not for a home you don't want to leak.

I'd lay down rubber on the roof immediately because it looks true and it is cheap and leak free.  Then at least you can build more carefully without worrying about it, because a leak will ruin the rafters beneath it in no more than a year or two (trust me).  You can build asphalt over this eventually, it's only one layer.  I'd chink the outside from the inside with spray foam until you get rid of 100% of the infiltration.  You can actually let your stove get smoky, blow a big fan inward from the door, and see what cracks the smoke blows out in order to help facilitate this.

Then I'd start building the insulation framing with studs and thick rigid insulation.  I like rigid because it doesn't allow bedding or spaces for the mice and water won;t mat it if you ever have a problem., You can fill the edges with foam.  Then wainscotting paneling over.  There are machines in Mother Eearth News you could buy that would let you rip this,  For walls and ceiling.

Floor:  A crawlspace foundation would let you be dry and to stuff insulation up under the floor rafters, or go without, the ground is reasonably warm.

Mice control will require a tight foundation and a cat.