Posted by admin | Posted in General | Posted on 27-12-2011
Open Wall construction isn’t restricted to just one technique. The theories and principles behind the development are unique, but the design uses existing methods and materials to match complete flexibility.
Methods discussed later describe only one of the quantity of design models created, and provides examples of the applications, that ought to be modified to satisfy local codes and personal preferences.
Wrap and Strap Open Wall Construction
This method is fantastic for tradesmen because its application is straightforward, and also the buildings thermal envelope can easily be maintained. It consists of a primary shell, which is the buildings structural skeleton, being constructed with standard platform framing techniques. The whole building will be wrapped in polyethylene, then a second non-structural skin is connected to the exterior, which is insulated and handle. This kind of open wall construction can be used to retro-fit existing two by four construction into super-insulated, air tight homes.
Platform Open Wall Construction
Platform construction methods require the framing carpenters perform not only the structural framing, but install the windows, doors, insulation, air/vapor barrier, exterior moisture barrier and sometimes exterior finishes when utilized in paneled wall sections.
This method has been utilized in the pre-manufacture of exterior walls in sections that are handled by four workers easily. It’s very effective for consumers, unfamiliar with structural design, but who would like to erect their own homes. It’s also a much quicker method because the building can be factory built elsewhere, shipped, and erected with the vapor barrier, insulation, electrical, interior finishes, windows, doors and siding already installed. A distinctive ability of the method is the capability of the structure to be disconnected and moved in sections. This would have ideal applications for modification and additions, or to perform panel repair/replacement.
Construction of pre-manufactured walls are made in major sections of eight foot lengths, and minor sections, in divisions of 1, two or four feet. Corner units are constructed to match varying exterior wall thickness. Wall heights include above floor thickness to keep interior ceiling heights of seven foot six inches to nine feet.
Foundation
When building the foundation wall assemblies, it is important to use proper materials and think about the utilization of a raised, compacted sub-footing. Whether using a granular sub footing, a full height concrete footing or a footing and sub foundation to elevate the wall assembly, the building blocks panels cannot be backfilled more that three and a half feet. Any more than this and the structural integrity from the wall will be compromised.
Foundation walls should also be constructed with at least two by eight inch plates to prevent lateral plate failure brought on by earth pressures. The bottom plate is of pressure treated material that is about a quarter of an inch smaller than non treated construction lumber. Because of this, the interior structural two by three wall assembly must overhang home plate by approximately one quarter inch. Exterior wall framing can be created with economy or number 3 graded lumber as long as it is pressure treated to resist rot. The horizontal economy grade stabilizer and remaining stud grade plates are non-treated lumber.
The inside framed two by three wall is constructed first. It’s constructed with regular framing nails using the studding at sixteen inch centers. The wall section will be squared off and secured to avoid movement. Over this, a polyethylene air/vapor barrier is positioned, with the edges folded within the outer wall members, and stapled along the outside faces. Do not staple the air/vapor barrier towards the edges of the plates or the studs, this will only punch irreparable holes inside it. Corner sections require that the air/vapor retarder be wrapped around the interior walls corner studding. Only at that connection it’s important to make sure that an adequate amount of the air/vapor barrier remains in order that it will provide a surface to seal to at the interconnecting sections. Corners ought to be neatly folded to avoid bunching which may create air passages and prevent proper joining of the sections.
Over this, a horizontal stabilizer is laid down perpendicular to the wall studding, and fastened with screws to each individual stud. The stabilizer ought to be placed forty-five inches above the sole plate for full batt insulation placement. The composite wall top plate can then be fastened to the interior wall top plate, flush and true, with normal ardox framing nails.
Individual pressure treated exterior wall studs may then be nailed to the to top plate at sixteen inches on center. Pressure treated sill plate is fastened, first towards the exterior studding, then the sole plate of the interior wall assembly, the two end studs, then all exterior wall studs. These studs should be arranged straight, and fastened towards the horizontal stabilizer with wood screws. Structural wind bracing (when needed) is placed within the wall section, when you are let into the exterior wall studs.
Batt insulation is laid in the middle cavity, perpendicular towards the studs with approximately one half-inch overhang in the ends of the wall assembly. Batt insulation can now be placed inside the exterior stud cavities. Depending on the covering of exterior, foam insulation as well as sealed polyethylene to grade is used. If foam insulation is used, the joints are sealed with vapor tape or acoustical sealant to the wood wall components in addition to one another. It’s a good idea to install the walls vapor trap along with the exterior polyethylene, like a single sheet, which can be sealed towards the interior vapor barrier between your two sole plates. A moisture barrier is then placed over the wall assembly. It’s secured by folding the perimeters over the studs and plates, and fastening with staples.
Finishing the wall by installation of the pressure treated plywood foundation cover and/or siding is then done. The plywood foundation paneling must be installed using the joints staggered from the underlying foam board. These panels are fastened with exterior screws, spaced eight inches round the edges, and ten inches within the interior area.
Foundation vapor traps and groundsheets ought to be sealed by sandwiching them between the sill plate and the the surface of the foundation having a combination of sill gaskets and acoustical sealant. The moisture barriers are sealed with vapor tape at each joint. Anchor bolts ought to be left loose to match shimming or grouting if necessary.
The outside walls are fastened together with wood screws, every two feet along the end studs of the interior wall. If neccessary, metal tie straps are installed on the interior edge of the top plate. The walls may then be leveled and squared before proceeding with floor or roof construction.
First Floor Walls
In design, it is crucial that if you do not use tie straps to keep the sections together, then your lower and upper sections must have overlapping plates to avoid separation. Also, depending on the particular design, the ground might have to be installed before continuing. It is recommended to install floors before continuing for this provides the carpenters a level area to create the upper walls on and supports the exterior foundation.
One way these walls could be installed when the windows are and siding is by overhanging the wall sections. Construction of the interior bearing walls, vapor barrier, stabilizer, plates and exterior wall studding within this approach is comparable to the foundation wall assembly. Where they differ is in the edging from the units.
Edging may be the bottom cover, which hides and protects the overhanging framed members and insulative barrier. It may be decorative hardboard nailed towards the underside from the sole plate that is sandwiched between the plate and also the foundation or floor assemblies. This edging should be sealed to both first floor and foundation wall or to the floor assembly vapor barriers.
This overhang technique is ideal when combined with a face brick applied around the first floors exterior. The overhang enables installation of bearing, platform framed floor assemblies while providing sufficient second story overhang for that brick face.
Doors and windows (exterior openings)
Probably the trickiest area to seal against infiltration and exfiltration. Even though area surrounding the outlet could be sealed with expanding foam, by pre-installing the windows in frames with a perimeter gasket, less work and material is required.
The window or door is first squared off in the frame, and locked in place by cross corner strapping. A half-inch plywood or aspenite frame is made up around the window. The aspenite frame width ought to be equal to the whole thickness from the wall assembly. This frame is then sealed to the window by sandwiching a sill gasket between it and the surrounding wood members, that is secured with wood screws inserted with the window frame. This allows removal for future repair or replacing a window or door. Leave approximately two inches from the gasket extending past the interior edge. The resulting box allows fastening of the interior finish directly to its surface, without gaps or unsupported areas.
The framed walls and header ought to be attached with screws directly to the boxed window, with sealant applied between your box and the individual vapor barriers. After squaring up the completed section, bracing is let into the studs. This bracing is important to the operation of windows or doors, because from square or twisted framing will cause binding. For this reason, casement windows and wood doors should be used to allow post construction adjustment. When the bracing has been secured, exterior sheathing with the moisture barriers are installed together, and exterior finishes applied.
Interior Floors
Because open wall construction relies on continuous wall insulation between stories, the interior floors within this method should be made to remain within the building envelope. Utilizing overhanging walls, wider lower wall sections or ledger strips, the inside floors could be supported on sufficient bearing. Floor assemblies can be joists, truss floors, wood I beams or any other kind of framing material.
Floor construction, through wall overhang or wider lower wall sections, allows the carpenters to construct the floor assemblies as current accepted practices, with one exception. The header or trimmer joist might have to be placed inside the edge of the top plate from the lower wall. The main anxiety about this type of construction is the fact that when installing of the upper-framed wall is attempted, there is a likely hood of dropping the low wall from the platform and foundation wall when raising it. Simple blocking or tiebacks underneath the floor may prevent this type of problem and ensure site safety.
Floor construction with ledger strips or ribbon boards permit finished floor levels to satisfy with the top plate of the lower wall assembly. The bearing ledgers or ribbon boards should be installed according to local building code requirements. Floor sheathing must overlap the wall joists to make sure an effective firebreak between floor levels. Although time intensive, header and trimmer joists could be omitted because end restraint is achieved by lamination to the lower wall studs.
Variations from the interior floor support concepts can include second plates, joist hangers or tie straps. Most significantly, design the connections for the tradesmen abilities. Framed floors are easiest to construct and install because the techniques and design criteria already exist. Only qualified personnel with the proper experience should attempt other more complex designs.
Roofs
Open wall construction was designed to be used with truss components, but by strapping over ceiling joists, exactly the same results can be obtained. For effective design, overhangs ought to be completely eliminated. They are costly and require extensive labor to complete. Roof edges should have angled fascia (called knife edging) to permit enough overhang to prevent excess run off from running down walls. Simple “two by” fascia, lapped over wall siding can be trimmed or painted in many colors and still provide adequate visual separation from the roof. By lapping the fascia over the siding gravity water cannot enter the buildings wall cavities. But don’t forget to leave enough screened eave area, to match adequate attic ventilation. Gables should also be completed with knife edging and reduced overhang. Sheathing and roofing materials are applied according to current building techniques.
Raised heel trusses or plated ceiling joists will raise the roof to allow for eave insulation and venting. The attic vapor barrier should consist of 10-millimeter polyethylene. This thicker and more durable layer is not as likely to become damaged during construction, or when running fish tapes for future utility lines. The vapor barrier is installed parallel towards the truss members or ceiling joists. Wall edges are sandwiched with acoustical sealant between your top wall plate and 2 by two strapping. Joints landing on truss members or ceiling joists should be sealed between it along with a bit of two by two strapping.
