Vinyl Window Considerations

By Gary Johnson

General

Vinyl framed windows have become the window of choice for the residential market for a number of reasons. Costs have become competitive with metal-framed assemblies, thermal performance is good especially in comparison to metal assemblies, and lastly, structural strength and quality control has improved over earlier products. Following are a number of considerations to be made when selecting a vinyl framed window assembly:

Vinyl

Not all vinyl materials are equal. A good quality vinyl will have a consistent chemical makeup and stable plasticizers. Ensure that the vinyl used does not incorporate recycled material as this makes quality control very difficult. Compare wall thicknesses of vinyl between competing products. Thicker walls are obviously stronger and are a good indication of quality.

Care must be taken to ensure compatibility of components during installation of the assembly as solvents in items such as bituminous membranes and caulking may attack the vinyl.

Chambers

The frames are produced using an extrusion process. The strongest assembly would be one where the frame is solid vinyl, however, this is obviously not the most practical. In order to reduce the amount of material the extrusions are hollow and webs within the extrusions form chambers that provide strength and improve thermal resistance. The number of chambers is determined by counting the spaces separating the exterior face of the frame from the interior face. There may be as few as a single chamber or as many as five. Generally the more chambers the better, both for rigidity and thermal performance.

It is important that the surface to which the glass is glazed be as rigid as is practical to reduce stress on the seal and thus improve the service life. A thin single walled flange is obviously not as strong as a multi-walled flange.

As vinyl has little screw holding power all hardware should be attached through a minimum of two webs

Reinforcement

Metal reinforcing channels can be inserted in the chambers to improve the structural performance of the assembly, especially those with large lights and/or operable vents. It is preferable that window hardware be attached to metal reinforcement. Metal reinforcement is another indication of quality.

Joinery

Vinyl has an advantage over other frame materials such as wood or aluminum in that the joinery (head/jamb, jamb/sill connections) can be welded, providing a long term, very watertight seal. Of course the effectiveness of the weld depends on the thickness of the material and the care taken to avoid racking of the frames during transportation and installation. Conversely, the joinery at intermediate mullions requires more care and maintenance then that of other materials because these connections cannot all be welded and sealants do not adhere well to vinyl. If at all possible intermediate mullions should be avoided.

Considerations Affecting All Windows (not just vinyl):

CSA A440 Window Standard

Part 5 of the Provincial Building Code requires that a window meet the minimum performance standards as set forth in CSA A440. This is a minimum requirement and a higher performance rating than that recommended in the code is wise. The “A” rating refers to air tightness and ranges from A1 (lowest) to A3 (highest). The “B” rating refers to water penetration resistance and ranges from B1 to B7. The “C” rating refers to wind load resistance and ranges from C1 to C5. There are other ratings but these three are the most important.

Moisture Management Approaches - Face Seal, Concealed Barrier, Rain Screen

Without going into a long involved explanation as to the differences (see discussion on frame design below), suffice it to say that a face sealed assembly is not as efficient as an assembly designed on rain screen principles. A concealed barrier approach is somewhat better than a face seal, however, the perimeter seals of the sealed glazing unit are usually left exposed in such assemblies, significantly shortening the sealed unit service life.

Where an assembly is well protected from the elements a face seal may be all that is required. In more exposed locations, such as a coastal site or a high rise, a rain screen assembly would be required if reasonable performance is to be expected. The A440 B rating (1 to 7 (best)) is an indication of the effectiveness of the moisture management system.

Glazing Method

Wet Glazing – relies on adhesion of the glazing material to the glass and to the frame. Since butyl tape does not adhere well to vinyl most (if not all) wet glazing is done with structural foam tape.

Dry Glazing – relies on compression of a resilient gasket to provide the seal. Rubber materials (EPDM, neoprene) have significantly better performance (due to long term resiliency) than vinyls and vinyl composites (Santoprene). Configuration of the gasket will also affect long-term performance. Gaskets should have multiple fins and be carefully fitted in the corners. Co-extruded gaskets (i.e. fins that are attached to the vinyl when the vinyl section is extruded) should only be used on replaceable glazing stops not the main frame of the window. Dry glazing is usually an indication of good quality.

Frame Design

A frame may be designed to receive glazing from either the exterior or interior. Usually a snap-in stop is installed to hold the glazing against the glazing bar (or the front or back of the glazing pocket as the case may be). The stop usually provides compression on the glazing tape or gasket to affect a seal.

A face-sealed assembly typically would be glazed from the interior and the exterior glazing tape would be expected to stay watertight for the life of the sealed unit. This type of unit can be expected to require regular maintenance. Subsill pan flashing should be provided to intercept the inevitable leakage from this type of frame.

Some economical assemblies use a concealed barrier approach. This assembly is glazed from the exterior. The exterior stop may or may not provide compression on the glazing seal located at the inside face of the sealed unit. This exterior stop is usually designed and installed such that it provides little in the way of weather protection for the glazing pocket. Drain holes are usually at the same level (or even higher) as the bottom of the glazing pocket allowing as much water and debris in as it allows out. Moisture held against the seals of a double glazed unit will usually cause the unit to fail prematurely. This approach also allows water to stand against the critical jamb/sill connection increasing the chance of leakage. (In a vinyl assemblies this is of particular concern at intermediate mullions.) Subsill pan flashing is required to intercept the inevitable leakage.

Some assemblies are “pocket glazed” – only one edge of the frame has a removable stop (usually the sill or the head). Compression on the glazing seals relies on the resiliency of the glazing gaskets themselves. Most of these assemblies have poor air and water tightness performance ratings and are only recommended for minimum exposure conditions.

Higher quality windows usually incorporate rain screen principles in the frame design. The assembly may be exterior or interior glazed. The outer seal is intended to prevent the vast majority of the water from gaining entry to the glazing pocket. If the moisture does defeat this seal the glazing pocket is drained through a baffled opening. The baffle prevents water and debris from entering the pocket. The drain opening also provides for pressure equalization across the exterior seal reducing the water penetration forces working against this seal. The inner seal acts as the final water and air barrier. Because this seal is protected from the elements this design’s service life is considerably longer than the other configurations described above.

Venting Units

Operable sash (vents) can be sliders, awning, hopper or casement. A slider is the most difficult to seal properly because there is little or no compression on the seals and they are subject to frictional wear. It is important to ensure that the seals on the slider are easily replaceable. The seals themselves are usually pile strips. The better pile strips will have a plastic fin that helps to affect a better seal.

Awning, hopper and casement windows have compression seals and are therefore superior to a slider. As with the glazing gaskets rubber seal material is superior to vinyl and vinyl composites because of its resiliency. The size and design of the bulb gasket will have a bearing on its efficiency and durability. Pile should never be used for a compression seal.

As with frame design a vent can be face sealed, concealed barrier or rainscreened. A face sealed or concealed barrier assembly will usually have only one line of seal. A rainscreened assembly will have two or more lines of seal.

Hardware for venting units can vary widely in function and performance. The hardware may be as simple as a hinge and latch or as elaborate as a tilt-turn function and multipoint latching. Ensure that operating hardware is installed in a manner that does not affect the seals around the operating sash. (Ensure that the A440 tests results include the operating hardware specified.)

Frame Installation

Residential windows for new construction are usually equipped with nailing flanges. For renovations new windows are usually rebate mounted. The method of installation is usually quite complicated requiring considerable thought as to how and in what order the various components are incorporated in the assembly. It is particularly important to ensure the subsill flashing is drained to the exterior. The air/vapour/water seal is usually provided by a self-adhesive membrane that is connected to the rear of the frame by a trim angle and caulking. Caulking materials containing solvents must not be used directly against the rubberized asphalt in the membrane as this may leach out bituminous materials causing unsightly black stains. Only acrylic latex caulking should be used at this connection.

Thanks to --- CMHC for the illustration and permission to use the material
Gary Johnson is a technical specialist located in the Victoria office of RJC. He brings over 30 years of building science and design experience.


	Vinyl Window Considerations By Gary Johnson General Vinyl framed windows have become the window of choice for the residential market for a number of reasons. Costs have become competitive with metal-framed assemblies, thermal performance is good especially in comparison to metal assemblies, and lastly, structural strength and quality control has improved over earlier products. Following are a number of considerations to be made when selecting a vinyl framed window assembly: Vinyl Not all vinyl materials are equal. A good quality vinyl will have a consistent chemical makeup and stable plasticizers. Ensure that the vinyl used does not incorporate recycled material as this makes quality control very difficult. Compare wall thicknesses of vinyl between competing products. Thicker walls are obviously stronger and are a good indication of quality. Care must be taken to ensure compatibility of components during installation of the assembly as solvents in items such as bituminous membranes and caulking may attack the vinyl. Chambers The frames are produced using an extrusion process. The strongest assembly would be one where the frame is solid vinyl, however, this is obviously not the most practical. In order to reduce the amount of material the extrusions are hollow and webs within the extrusions form chambers that provide strength and improve thermal resistance. The number of chambers is determined by counting the spaces separating the exterior face of the frame from the interior face. There may be as few as a single chamber or as many as five. Generally the more chambers the better, both for rigidity and thermal performance. It is important that the surface to which the glass is glazed be as rigid as is practical to reduce stress on the seal and thus improve the service life. A thin single walled flange is obviously not as strong as a multi-walled flange. As vinyl has little screw holding power all hardware should be attached through a minimum of two webs Reinforcement Metal reinforcing channels can be inserted in the chambers to improve the structural performance of the assembly, especially those with large lights and/or operable vents. It is preferable that window hardware be attached to metal reinforcement. Metal reinforcement is another indication of quality. Joinery Vinyl has an advantage over other frame materials such as wood or aluminum in that the joinery (head/jamb, jamb/sill connections) can be welded, providing a long term, very watertight seal. Of course the effectiveness of the weld depends on the thickness of the material and the care taken to avoid racking of the frames during transportation and installation. Conversely, the joinery at intermediate mullions requires more care and maintenance then that of other materials because these connections cannot all be welded and sealants do not adhere well to vinyl. If at all possible intermediate mullions should be avoided. Considerations Affecting All Windows (not just vinyl): CSA A440 Window Standard Part 5 of the Provincial Building Code requires that a window meet the minimum performance standards as set forth in CSA A440. This is a minimum requirement and a higher performance rating than that recommended in the code is wise. The “A” rating refers to air tightness and ranges from A1 (lowest) to A3 (highest). The “B” rating refers to water penetration resistance and ranges from B1 to B7. The “C” rating refers to wind load resistance and ranges from C1 to C5. There are other ratings but these three are the most important. Moisture Management Approaches - Face Seal, Concealed Barrier, Rain Screen Without going into a long involved explanation as to the differences (see discussion on frame design below), suffice it to say that a face sealed assembly is not as efficient as an assembly designed on rain screen principles. A concealed barrier approach is somewhat better than a face seal, however, the perimeter seals of the sealed glazing unit are usually left exposed in such assemblies, significantly shortening the sealed unit service life. Where an assembly is well protected from the elements a face seal may be all that is required. In more exposed locations, such as a coastal site or a high rise, a rain screen assembly would be required if reasonable performance is to be expected. The A440 B rating (1 to 7 (best)) is an indication of the effectiveness of the moisture management system. Glazing Method Wet Glazing – relies on adhesion of the glazing material to the glass and to the frame. Since butyl tape does not adhere well to vinyl most (if not all) wet glazing is done with structural foam tape. Dry Glazing – relies on compression of a resilient gasket to provide the seal. Rubber materials (EPDM, neoprene) have significantly better performance (due to long term resiliency) than vinyls and vinyl composites (Santoprene). Configuration of the gasket will also affect long-term performance. Gaskets should have multiple fins and be carefully fitted in the corners. Co-extruded gaskets (i.e. fins that are attached to the vinyl when the vinyl section is extruded) should only be used on replaceable glazing stops not the main frame of the window. Dry glazing is usually an indication of good quality. Frame Design A frame may be designed to receive glazing from either the exterior or interior. Usually a snap-in stop is installed to hold the glazing against the glazing bar (or the front or back of the glazing pocket as the case may be). The stop usually provides compression on the glazing tape or gasket to affect a seal. A face-sealed assembly typically would be glazed from the interior and the exterior glazing tape would be expected to stay watertight for the life of the sealed unit. This type of unit can be expected to require regular maintenance. Subsill pan flashing should be provided to intercept the inevitable leakage from this type of frame. Some economical assemblies use a concealed barrier approach. This assembly is glazed from the exterior. The exterior stop may or may not provide compression on the glazing seal located at the inside face of the sealed unit. This exterior stop is usually designed and installed such that it provides little in the way of weather protection for the glazing pocket. Drain holes are usually at the same level (or even higher) as the bottom of the glazing pocket allowing as much water and debris in as it allows out. Moisture held against the seals of a double glazed unit will usually cause the unit to fail prematurely. This approach also allows water to stand against the critical jamb/sill connection increasing the chance of leakage. (In a vinyl assemblies this is of particular concern at intermediate mullions.) Subsill pan flashing is required to intercept the inevitable leakage. Some assemblies are “pocket glazed” – only one edge of the frame has a removable stop (usually the sill or the head). Compression on the glazing seals relies on the resiliency of the glazing gaskets themselves. Most of these assemblies have poor air and water tightness performance ratings and are only recommended for minimum exposure conditions. Higher quality windows usually incorporate rain screen principles in the frame design. The assembly may be exterior or interior glazed. The outer seal is intended to prevent the vast majority of the water from gaining entry to the glazing pocket. If the moisture does defeat this seal the glazing pocket is drained through a baffled opening. The baffle prevents water and debris from entering the pocket. The drain opening also provides for pressure equalization across the exterior seal reducing the water penetration forces working against this seal. The inner seal acts as the final water and air barrier. Because this seal is protected from the elements this design’s service life is considerably longer than the other configurations described above. Venting Units Operable sash (vents) can be sliders, awning, hopper or casement. A slider is the most difficult to seal properly because there is little or no compression on the seals and they are subject to frictional wear. It is important to ensure that the seals on the slider are easily replaceable. The seals themselves are usually pile strips. The better pile strips will have a plastic fin that helps to affect a better seal. Awning, hopper and casement windows have compression seals and are therefore superior to a slider. As with the glazing gaskets rubber seal material is superior to vinyl and vinyl composites because of its resiliency. The size and design of the bulb gasket will have a bearing on its efficiency and durability. Pile should never be used for a compression seal. As with frame design a vent can be face sealed, concealed barrier or rainscreened. A face sealed or concealed barrier assembly will usually have only one line of seal. A rainscreened assembly will have two or more lines of seal. Hardware for venting units can vary widely in function and performance. The hardware may be as simple as a hinge and latch or as elaborate as a tilt-turn function and multipoint latching. Ensure that operating hardware is installed in a manner that does not affect the seals around the operating sash. (Ensure that the A440 tests results include the operating hardware specified.) Frame Installation Residential windows for new construction are usually equipped with nailing flanges. For renovations new windows are usually rebate mounted. The method of installation is usually quite complicated requiring considerable thought as to how and in what order the various components are incorporated in the assembly. It is particularly important to ensure the subsill flashing is drained to the exterior. The air/vapour/water seal is usually provided by a self-adhesive membrane that is connected to the rear of the frame by a trim angle and caulking. Caulking materials containing solvents must not be used directly against the rubberized asphalt in the membrane as this may leach out bituminous materials causing unsightly black stains. Only acrylic latex caulking should be used at this connection. Thanks to --- CMHC for the illustration and permission to use the material Gary Johnson is a technical specialist located in the Victoria office of RJC. He brings over 30 years of building science and design experience.

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