Wednesday, June 1, 2016

Construction - Pre-made Exterior Window-Housing Wall Sections

After considerable research on windows and doors, I decided in favor of Pella fiberglass casement windows and fiberglass doors. (For more details on window selection, see a previous post on window design.) The building code specifies that the total window area be at least 8% of the livable floor area.  Furthermore, 4% of the windows must be operable plus egress-friendly in rooms, such as bedrooms, that do not otherwise have direct access to the exterior.  Our passive solar design that situates all but one small east window in the south wall meant that, to meet code, the windows would have to be large and bunched together.  We meet code by utilizing 9 pairs of windows plus one unit of three windows with each window 3' wide and either 5' or 6' tall.  The size of the windows automatically render moot the egress requirement.

The Pella rep was somewhat taken aback when I specified individual windows instead of enjoying the advantage of pairs of windows being joined at the factory with fiberglass mullions as is typical. There are a couple of reasons for keeping them separate.  First, it would be impossible for me, working alone, to install two heavy windows in one piece -- even the individual windows will be a challenge. Second, cost is reduced by about 10%.   

So let me share how I went about using mostly downtime caused by bad weather to assemble in the shop the wall sections that will house the windows.  Eventually, the sections will in interspersed with individual trusses for a wall thickness of 15" insulated with rice hulls to an R-50.

Jigs To Standardize the Wall Sections
Fortunately, there was enough room on all sides of the table saw to use it to support a jig of about 7' x 8' in size.  I would have preferred to use salvaged lumber for the jig but quickly learned that it was too non-standard. Therefore, I used new lumber to insure that all wall sections would be identical -- square, plumb and level.  And I found out by trial and error that it would take mostly new lumber to standardize the wall sections as well.

It took two jigs to make a wall section.  The first one on the saw (top photo) was used to cut and fit the side of the assembly facing the interior of the house then the cut pieces were disassembled and set aside. Then the same jig was used to cut and fit the side facing the exterior which varied with the interior assembly only in the window sill area.  

The next task was to join the interior and exterior assemblies.  This was done by removing from the saw-top jig the 2 x 4 on the left side of the exterior assembly and matching it with
the left 2 x 4 for the interior assembly that had been set aside earlier. They were transferred to the truss jig that was described in detail in a prior post on wall trusses (second photo).  The left interior and exterior 2 x 4s were nailed together to form a truss then the truss was moved  back to the saw-table jig. The right interior and exterior 2 x 4s were similarly nailed together in the truss jig and returned to the saw-top jig. The final step was to fasten all of the individual pieces together in the saw-t jig to make a three dimensional wall section.

Storage
The wall sections will not be needed for a couple of months so it became imperative to protect them from the elements, particularly since some of the gussets for the trusses were OSB.  I tried first to wrap them in stretch wrap but soon realized that was folly -- it was hard to accomplish and it leaked even in light rain. Instead we moved all of the sections onto the house floor and thoroughly enclosed them with plastic and battened-down tarps.  

The OSB pieces that will line the window openings were cut and stored separately with the intention of adding them later after the walls are raised, thereby reducing the weight of the sections for easier handling and delaying their exposure to the elements as long as possible.  In the same vein, I am erecting the weight-bearing interior walls before assembling the exterior truss walls so as to be able to get the exterior walls under cover as soon as possible after they are in place.

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