Would Bensonwood’s wall assemblies classify as the perfect wall?
geran_brown
| Posted in General Questions on
Hi,
My wife and I are in the planning phase of building our own home (Climate 4A, Maryland). I would like to use preassembled panels if possible. One of the options we are considering is Bensonwood on a slab.
I was wondering based on the attachment below if their walls would be considered a perfect wall assembly (as long as the seams and joints are sealed correctly)?
The other options we are looking at are Ecocor or BuildSmartNA panels.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
There is more than one way to build a perfect wall.
BSC version and the one you are referring to is to put all the control layers in the same plane and add a layer of wind and water impervious rigid insulation on top of it. The benefit of this wall is that it is really simple to build if you need a thin layer of exterior insulation. On the other hand, rigid insulation is expensive compare to batts and loose fill insulation. Also, putting more than 3 or 4'' of rigid insulation on a wall is painful.
The european way and the one Bensonwood use is to build a layer of continuous insulation with wall trusses (typically larsen trusses or i joists). This way you can build a thick wall quite easily with as much insulation as you want since you can make the trusses as deep as you want. This also means you can use loose fill or batt insulation which is much cheaper than rigid insulation. The downside is now you need another control layer on top of your insulation because this type of insulation is not wind tight. Wind going through your outside insulation would greatly reduce its R value so you need to stop it. Plus, since the trusses are build from wood, you also need to protect them from the rain so the water control layer has to go on top of these trusses. So to summarize, you'll have a control layer on top of the continuous insulation acting as a water and wind control layer. The control layer behind the insulation now just need to act as a vapor and air control layer so interior moisture can't condensate in your wall. It doesn't have to control water anymore since the layer on top of the insulation is the one doing it. The top layer is usually a permeable membrane like the siga Majevest or the Proclima Mento and the interior air membrane is just the sheating taped with an acrylic based tape.
So in my opinion, you should figure out how much continuous insulation you need in your climate zone and choose from there. Adding one layer of rigid insulation to a wall is pretty easy if you decide to do it yourself. Building trusses is a bit more work so prefabricated walls are a good option.
Hope it makes sense. It's not easy to summarize everything in 1 or 2 paragraphs :-)
" It's not easy to summarize everything in 1 or 2 paragraphs"
I think you did a really good job!
I think the essence of the "Perfect Wall" is that the structural framing of the home is entirely within the conditioned space. The air barrier and thermal layers are on the exterior allowing the framing to remain at a constant temperature and moisture level- allowing the building to last 'hundreds of years'.
The Bensonwood walls would not fall under this design as some of the structural elements are near the exterior. Nevertheless, Bensonwood makes a damn good wall and I wouldn't have any reservations about using them, personally.