The Double-Stud Wall Simplified
Low Cost, High Performance
Simplify.We know pushing standard code-minimum construction toward high performance is complicated. So we're always looking for ways to simplify - to simultaneously reduce cost while optimizing efficiency and occupant comfort. See our post on Breaking The "Upfront Cost Barrier". The double-stud wall is a well established method for creating a very economical, durable and high R-value assembly in new construction. This type of wall can be built quickly with standard methods and keeps the material pallet very simple when compared to other thick wall assemblies (studs, one type of insulation, membranes + tapes). Integrated with Pro Clima airsealing and moisture control components, the double-stud wall provides unmatched economic value, safety from moisture damage, and long-lasting performance.
Design ElementsWith Pro Clima component integration, we're taking it one step further. Below we illustrate a sheathing-less double-stud wall (that's right: no structural sheathing) that provides the following characteristics:
- Minimized material costs
- Maximized moisture drying potential
- Removal of formaldehydes, VOC's and other toxic chemicals readily found in SPF, rigid foams, OSB and plywood
- Easily adjustable wall thickness to meet your design R-value.
- Space between walls for continuous insulation
- Utilization of dense-pack insulation (cellulose, fiberglass, mineral wool or sheepswool) - or smartly stack batts (see this project).
- No special materials or connections needed for the framing component
- Fits with the typical platform framing method
The elements of a cost efficient double stud wall assembly: Interior perspective
Down To The BasicsThe wall consists of an outer load-bearing wall and an inner finishing wall. The floor and roof loads are stacked on top of the outer wall studs. This advanced framing method can allow in certain cases use 24" o.c. assembly if your floor and roof loads meet the design criteria. The outer wall is framed like any other stick-built wall, with the exception that the shear load is carried by 2x lumber nailed diagonally to the back side (in the insulation cavity). It's important to note that each structure will have very different shear and uplift retention requirements due to variables in building height, # of windows, local codes, shape of building, seismic requirements, etc. The inner wall is connected to the deck and the underside of the trusses or joists. It requires minimal framing material and opening headers as it need only retain the insulation and carry the finishing surface (drywall). In taller walls, it's important to install a connect the inner and outer studs for additional strength as well as partition the bays every second bay - to make densepacking of the double stud cavities easier to quality control (reach proper density). The elements of a cost efficient double stud wall assembly: Exterior perspective The inner wall has one additional framing element: the service cavity. We consider the service cavity to be essential in this construction, for 5 main reasons:
- It provides room for pipes and wires to travel without multiple penetrations of the airtight layers
- It offers simple installation of utility boxes and light fixtures
- It protects the Intello Plus membrane from possible puncture once the wall is closed, as the drywall is a sacrificial layer
- Together with INTELLO Plus it supports the dense-packed installation with horizontal ledges - which helps distrubute the weight/pressure of the insulation at the INTELLO plus and provides best results for insulation density in walls.
- It provides an additional thermal break when the service cavity space is filled with insulation