[Strawbale] How to run chminey through strawbale wall?
ArchiLogic at yahoo...
Sun Sep 26 20:43:21 CEST 2010
On Fri, 17 Sep 2010 16:04:38 -0400, dirk witvrouwen
<dirk.witvrouwen at hotmail...> wrote:
> I'd like to know a safe way to run a woodstove chimney horizontally
> through a strawbale wall. I'm using a double walled stainless steel
> chimney (3cm mineral insulation between the two shells).
I'd say "Just don't (run a chimney through the wall).
I would say:
"Relocate the woodstove to a spot that is as close to the geometric centre
of the floor plan as is possible and run the chimney straight up through
the roof exiting as close to the ridge of the roof as is possible."
Keeping most of the chimney inside of the house minimises heat loss from
chimney to the cold outdoors, hence minimises the cooling that the chimney
will experience and that will minimise the opportunity for creosote
formation (assuming proper burning habits) and the risk of chimney fires.
Also, most of the heat loss through the chimney walls will be beneficial
to the conditioned interior living volume.
Also, if exiting through the wall results in the chimney being at the
eaves of a sloped roof and if the house is in a climate that receives snow
and if the roof cladding is metal, the potential for the chimmey being
knocked over by sliding ice and slow is created, not to mention the
increased potential for roof leaks around the chimney flashing, assuming
that the house is provided with reasonably wide overhangs to keep the SB
I could go on but basic point is "Why create potential problems ?"
assuming that the building is still either in the design stage or
But if the chimney *must* go through the wall, then I would cut a round
hole through the straw and then simply install wire mesh and a 50 mm
thickness of concrete (aka "Portland cement plaster) over the straw,
taking care to properly embed the mesh in the concrete to ensure that the
mesh will do its job of providing the tensile reinforcement necessary to
prevent cracking due to the thermal stresses to which the plaster chimney
hole lining will be subjected.
If necessary, I would install pieces of 11 mm thick OSB or plywood on the
inside and outside surfaces of the SB wall with matching holes cut in the
OSB to serve as temporary formwork, using an F-clamp or such-like to keep
the formwork in place. I would of course first cover the OSB or plywood
with salvaged polyethylene sheeting to facilitate easy form removal and to
help keep the mixing water in the concrete for as long as possible to
ensure full hydration of the cement during the curing process. I would
also insert a few strategically-placed anchor sleeves into the wet mud to
provide points of attachment in the hardened concrete for the sheet metal
cover/air barrier that will eventually go over the penetration.
Then I would install a sheet metal sleeve inside that plastered opening,
using non-combustible spacers to create an airspace of 50 mm or more
between the plaster and the sheet metal sleeve.
Then I would install more non-combustible spacers between the sheet metal
sleeve and the insulated chimney to create the manufacturer's specified
The sheet metal sleeve mentioned above functions as a radiant barrier and
the 50 mm air space behind it will help to minimise heat transfer to the
50mm thick concrete hole lining so that the potential for pyrolisis of the
straw adjacent to the concrete lining will be minimised.
Just in case it's not obvious, all of the sheet metal mentioned above
should be cut from corrosion-resistant (ie hot-dipped galvanised or
galvalume or stainless steel) flat stock of 26 gauge or thicker.
For the sheet metal cover/air barrier on the inside/outside of the
penetration, I would cut the hole about 12 mm smaller than the outside
diameter of chimney and peen over the 6 mm excess to the inside of the
hole. That peened-over edge will help to stiffen the opening in the sheet
metal cover and also provide a caulking groove (using a fire-rated
caulking of course ie "Dap Fire Stop" silicone.)
=== * ===
Kanata, Ontario, Canada
< A r c h i L o g i c at Y a h o o dot c a >
manually winnow the chaff from my edress if you hit "reply"
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
More information about the Strawbale