This is the third and last of three 'mirrored' pages of sections of the Web Site of the USA based IronStraw Group (Cashmere, Washington). Permission was received to copy the information on the pages. You can visit The IronStraw Group by clicking on the logo. More information about The IronStraw Group is provided at the bottom of this page.
This is the sixth section in this series about building strawbale homes.
The final part of building your strawbale home is getting a roof on top of your straw. In the last section we covered box beams (the top plate or rigid beam assembly - RBA) and tie-down systems. There is one final connection - your roof structure to the top plate of the wall (RBA).
With trusses we use a conventional rafter tie (hurricane clip) available at most lumber yards and manufactured by several firms, the most common is Simpson. The rafter tie is a metal angle bracket that nails horizontally to the truss and at 90 degrees, horizontally to the box beam or top plate thus making a strong connection that cannot be pulled apart vertically by wind uplift on your roof.
The photograph shows trusses on top of load bearing walls that have box beams as top plates. In the photo on the left the box beam has a piece of black asphalt paper covering it so the stucco does not contact the wood. There is also a piece of wood trim on the top inside edge of the box beam to stucco up to. The photo shows a 7-bale high wall with scissor trusses on 6' centers.
The roofing method you choose depends on your design; however, most roof structures and coverings for strawbale homes are conventional building materials and methods. A carpenter/framer/roofer can help you with this part of the building if you do not have enough volunteer help. The simplest style is a conventional flat bottom truss and 5/8" plywood sheathing. The plywood is being installed in the photo on the right above.
We prefer 5/8" over 1/2" plywood because the thinner plywood feels scary to walk on to us and we like the added solidness to the roof and the extra expense is small. Since all the roofing from here up on a strawbale is the same as in stick built homes, we will leave the choices up to you to decide based on your personal desires.
The photo on the right shows box beams at the very bottom of the photo on each side of the truss. This is a 2x4 box beam with trusses on 24" centers. There are lots of combinations for roof framing, we prefer trusses because they go up so fast. It is very important to get the load-bearing walls covered with a roof as quickly as possible. All the trusses in both photos were attached with rafter ties.
So the walls went up quickly and you've got the roof on and the straw's dry - what next?
There's still a lot of work to do to get your strawbale finished. Preparing the walls for stucco and making sure you have everything through the walls (like electricity, plumbing, gas, telephone) is next. All wood surfaces that will be covered with stucco need to be completely covered by have a piece of asphalt paper stapled to them so no stucco touches the wood.
Most strawbale homes have poultry wire stretched over the inside and outside surfaces. This is usually done to satisfy Building Officials and because wire is always needed in conventional stucco applications over wood. Again, the conventional stucco wire is about 17 Gauge and that is what is normally recommended. Most poultry wire (or called chicken wire) is thinner at 20 gauge. Since the wire is going over the straw and is not supporting the stucco, we have always used the more readily available thinner gauge.
The poultry wire is attached to the bottom sill plates and then stretched up to the top plate or box beam and attached to it. Usually we use 1 1/4" galvanized roofing nails. If you have access to an air compressor and a staple gun, they also work very well and are very fast. The wire may be installed vertically or horizontally - which ever way you feel is the easiest. The wire comes in rolls that are 4' or 5' wide. Overlap all joints 6" and clip together with "hog" clips.
The photo shows the poultry wire in place around a window. You may need to look closely, it is the very thin looking hexagonal wire. Also shown is expanded metal lath around the window frame (the heavier diamond shaped metal) and the asphalt paper covering the wood. Every window or door frame must be lathed with a 6" overlap of lath onto the straw. This is to prevent cracking at the joint between the wood and the straw. The metal lath can also be attached using galvanized roofing nails. The windows in the photo are solid vinyl and the stucco will be applied right up to the vinyl with no exterior trim needed.
Next time we'll go into stuccoing and some notes on interior finishing. Note by Project SafeCom: This section has as yet not been posted to the IronStraw Group's Web Site.
*NOTE: The photographs on these pages are from different homes and should not be taken as a complete detail of how to build your home. Please consult with us for any questions about this series of articles.
If you are interested in building, see our consulting page to see how we can help you. You can e-mail Michael Thomas, Co-Founder of IronStraw Group in the USA at thomas(at)ironstraw.org
For more information click on the IronStraw logo or e-mail
The Ironstraw Group at: info(at)ironstraw.org
P.O. Box 715
Cashmere, WA 98815