Hello fellow natural builders, This has been a interesting thread concerning two different issues on plastering straw bale buildings, so indulge me. The first is applying plaster directly on the bales with proper separation with different building material wood post etc. is the key to allow that expansion and contraction of different materials through the heating and cooling cycles. Here in the USA where I have designed over 20 straw bale homes in Colorado and Washington State, and built 14 of them since 1993 I have had zero stucco failure, abet the first home is only approximately seventeen years old in Colorado. So far I have had no call backs concerning rotten bales or failed flashing details etc. I have also inspected dozens of sb homes through the years, finding moisture issues failure based on poor construction habits from inexperienced home owners or builders. I believe that the success in any type of building is in good design & detailing whatever the building envelope is used. There's are many moisture studies for different plaster types for sb walls. One of which I was in the issue # 46 of the last straw journal by Candace Gossen a during a 7 year study in raining Portland Oregon where moisture was never higher than 12 percent located in the exterior 4" of the lower bales during summer where the delta T was the highest. Clay sand base coat, lime sand finish plaster on the exterior and interior were used. The Canada cmhc http://www.cmhc-schl.gc.ca/en/index.cfm has documented many plaster failures in SB homes. The imporatance of applying plaster directly to the bales is demonstrated in the fire testing by the EBN group at this link. A 2 hr fire rating for cement /lime plaster and a 1 hour fire rating for clay sand plaster. http://www.ecobuildnetwork.org/images/stories/FireTestVideo/EBNetFireTest.mov I feel using any type of sheathing for lateral loads losses that fire rated protection and one of the major benefits of building with straw bales. Here in the states conventional wood framing with plywood shear has a 20 mins fire rating, which I believe is a hazard & liability when building in fire prone areas or when it takes more than 5mins for the fire department to reach your home. Building in Washington State on the waterfront we have horizontal rain conditions with wind driven rain up to 85 mph (exposesure D =125 mph lateral loads) begs for protection for all types of building envelopes. I don't care what type of siding is used it will get through it with that amount of hydrostatic pressure. An old solution has been to install a rain screen between the siding and felt paper, to mechanically allow the water seepage to drain down the air space safely out the bottom at the water table. This works in all type of construction and is especial good detail for a severe weather location allows the siding to dry out. An SB wall would have a scratch and brown coat of plaster flush with vertical exterior pins, ( interior and exterior pins tied together stabilizing the straw bale walls transversely, vertical 1x2x3/4" 16" o.c. nailed to the top girder and bottom plate) I then install an emulsified impregnated paper (15 lb felt, installed horizontally with 6" laps attached to the vertical pinning. Add another 1x2x3/4" vertical pinning ( rain screen) over the SB exterior pinning and felt paper, creating a ventilation space. Siding can now be nailed to the vertical pinning. If plaster is to be used I would use a drainage plane mat (instead of the vert. furring ) with 2"x2" welded wire furred approximately to key the plaster. In areas where there will be a high amount of rain or snow that may contact the base wall, especially clay & sand, I always suggest an exterior 3-4' tall wainscoting of stone or brick for protection. It protected all of the Clay sand plaster on my Colorado Cottage, except a small 4"x12" area on a conventional wall with no eves. I'm curious about using SB for the roof insulation without an 1" air space to vent the heated moisture can anyone comment on this. I have seen this in europe, have the roofs been inspected for rot ? Thank you have fun building your straw bale home. Yahoo! Bruce Glenn Passive Solar Designer Builder 27+ yrs Healthy, Passive Solar, Energy Efficient Home Environments Straw Bale Pioneer since 1993, Twenty homes and counting! Creative Solutions for our Living World Terra Sol Eco Homes LLC The Green Builder Ask about our winter & summer straw bale, passive solar, workshops! wk 360-385-5477 cell 360-301-3150 Message: 1 Date: Mon, 06 Dec 2010 11:52:46 +0100 From: asbn <asbn@baubiologie...> Subject: Re: [Strawbale] OSB or Not? (rendering versus sheeting) (dirk witvrouwen) To: European strawbale building discussions Message-ID: <C9227F0E.1016A%asbn@baubiologie.at> Content-Type: text/plain; charset="ISO-8859-2" just an addition... > The question comes back to the basics; too much protection against > moisture movement sounds dangerous. No, I don't agree to this. This is building physics standard and can be calculated easily. You can eventually plaster directly on the inside but the problem is, that a direct plaster on the outside without a folie or other prevention against water & humidity (rainfall) on the facade often leads to problems within the insulation-layer. The reason is, that (in our areas) limeplaster is used, and this plaster sucks the rain, gets wet and so the insulation layer, if you have no really big overhangs in the roof. Earth-plaster on the outside in our rainy/snowy areas leads to a wash-out of the earth-plaster, as it can be seen on the loadbearing house in St. Georgen / Carinthia. First there are small hairy cracks which freeze in the winter and grow to big cracks, where the water runs in... So if you limewash your plaster every year (as you often see it in Greece) and have big roof-overhangs, you maybe will get no problems. But if you want to be sure and safe, that nothing happens especially in our areas (and especially on the weather side), you have to install a rainproof layer (folie or Agepan board or similar) on the facade under your plaster (or if the facade is shadowed by trees better use a ventilated wooden facade). You need this folie and board also for your windproofness... Mit lieben Gr??en Herbert Gruber -- asbn - austrian strawbale network ?sterreichisches Netzwerk f?r Strohballenbau 3720 Ravelsbach, Baierdorf 6 Email: asbn@baubiologie... |