Building with cement blocks?

HilltopDaisy · #1 09/10/05, 03:33 PM

I was talking with my brother about the cost of heating this winter, and he is suggesting adding a small room onto this old mobile for a wood stove. He says pour a 6" concrete pad and build entirely with cement blocks, add a woodstove and there you go. Could it really be that simple and inexpensive? The firewood will be free. I've never used cement blocks before, only built with lumber. Advice?

moopups · #2 09/10/05, 03:38 PM

For concrete blocks to stay where they are put for a long time the foundation needs to go below the frost line. Is that practical for you? A fire proof (internally) wooden structure is also acceptable for a wood stove.

gobug · #3 09/10/05, 04:03 PM

Hilltop
Considering that you are in NY, it is a good idea take moopups advice. You might find someone local to put the pad in. I don't know that it needs to be 6 inches. Since it would be small, a posthole to below freezing on each corner should be adequate.

The cinder block can be dry stacked (no cement mortar between the blocks) and surface bonded. A bag of surface bond cement applied according to the instructions would actually be stronger than one with mortar between the blocks. I think a bag runs about $10-12 here.

I can't imagine a cinder block roof, so I am thinking your brother didn't mean that. With a conventional wooden roof, you would need a flue. The roof and flue would probably cost more than the block and be more difficult to build. Do you already have the stove?

A fan to circulate the warm air would help spread the heat.

If you add up the costs: stove, flue, lumber, roofing, cinder block, surface bonding cement, and the concrete pad, you may be surprised how much it will be. While it may be difficult to add any insulation to walls and ceiling, it could be more cost effective to use foam board to cover your windows, and make your skirt tight.

Have you already done these things?
Gary

mtman · #4 09/10/05, 04:18 PM

they have cement blocks with the holes lined with styrofoam cut down on the dampness of the block

HilltopDaisy · #5 09/11/05, 08:52 AM

The frost line is 3-4' deep here in NY. Yes, we were thinking a wood framed roof, with a metal roof over plywood.

minnikin1 · #6 09/11/05, 09:56 AM

In the cob-oven book, there is a sample of a portable oven that is built on a trailer.

IF you build it to be a temporary thing, you might be able to use some of the ideas from that - and avoid the frost-line issue. You'd be able to do it quickly enough to get it going this year, too...
You would need a sand bed and either perlite or vermiculite to insulate the
"floor".
We have a lot of fiberglass insulation we're pulling out of the barn, let us know if you want some.
The insulation smells a little musty, but it's surely good enough for a wood stove room....

Explorer · #7 09/11/05, 10:34 AM

Good advice, but the question is not very clear. When you say a "small" room, how big are you planning. A room large enough to use for other things, say 8'x10' or just a very small room for the stove and maybe a little wood, say 4'x4'?

Explorer · #8 09/11/05, 10:41 AM

Good advice, but the question is not very clear. When you say a "small" room, how big are you planning. A room large enough to use for other things, say 8'x10' or just a very small room for the stove and maybe a little wood, say 4'x4'?

rambler · #9 09/11/05, 12:53 PM

You are going to get a lot of conflicting advise, because you didn't really tell us what you are trying to build. How big is 'small' to you, and what is the point of the room, just only the stove, or any other use? And how do you plan to move heat from it to the real house?

Since 6 inch floor is overkill, I will assume the advise you got was for a floating slab - built that thick for a small 6x6 biulding, the whole building will simply 'float' on the frost, no need for a foundation. Be aware: You may need a 'ratwall' around the edge to keep critters from burrowing under. If you hook any pipes or ductwork beween this floating building and your house (and you have to don't you?) they need to be flexable, as this building will move & raise & sink a few inches as the ground freezes & sinks. It is best to be on dry ground, a bit of gravel under to keep it more stable.

I'm not a fan of floating slabs, but they do work as long as you are aware they do shift a few inches a couple times a year. They need the strong floor & rebar to keep everything moving together.

If this is a furnace room, you really need to insulate it. Would be best to insulate the _outside_ of the building, and use the blocks for thermal mass. I don't think much of putting a stove inside an uninsulated block building - you will spend more wood heating the outdoors that getting anything useable.

And so on, but not sure what you are trying to build so I'll stop there.

--->Paul

HilltopDaisy · #10 09/11/05, 01:51 PM

8' x8' room, no ductwork, I'd use a small fan to move the heated air. Firewood is free.

Explorer · #11 09/12/05, 06:57 AM

In the 50's I lived on the high plains of western New Mexico and this practice was common. Folks would build an entry shed next to their mobile and install a wood stove. Wood was free from the nearby mountains and in plentiful supply. The shed was built on concrete piers about a foot high and then skirted like the mobile. Simple building, made of 2x4's with wood floor and covered with tar paper or rolled roofing on the top and sides. Entry was thru a new door and then into the mobile thru an existing door.

I do not recall how they were attached to the mobile, nothing fancy. Today I would use exterior expanding foam from a can to seal the opening between the shed and the mobile. Course then there were not any building code that was honored or building inspectors. Good luck as this sounds like a worthwhile project to you.