Yet some building enclosures failed anyway, full of moisture, rot and heartache. It was expensive and frustrating. We thought we were using great technologies to seal windows and protect openings from moisture. Our collective response was to over-engineer and overthink. But trying to protect openings from moisture by adding complexity opened the door to design flaws and installation defects.
The Cast of naked sin sealant joint white is easily inspected from the interior. These case studies Window flashing in block openings detailing methodologies for wood and metal block-frame window frames and concrete wall openings applicable for new and existing exterior wall systems. The result of this necessary use bloc, through-wall flashings made it impractical to use opemings windows and doors at punched openings. Two case studies summarize the details of design and retrofit installation for sill pan flashing of replacement block-frame window into the perimeters of existing recessed concrete wall openings. What we eventually realized is that no bulwark of tapes and sheets can beat the reliability of a properly installed liquid-applied flashing. Here is the key point.
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Abstract: Integrating sill pan window flashing can be challenging using block-frame windows or installing flashings within a recessed opening in a concrete wall.
A little bit of history…back in the day the United States was known for its manufacturing prowess . Yup, bad pun…intended. So how come it gets so complicated?
Well, not all walls are alike. Not all windows and doors are alike. Not all water and air control layers are alike. There are good reasons for this. The walls are easy. The issue is connecting the windows and doors to the walls…specifically to these layers in the walls. We have both flanged and unflanged windows and flanged and unflanged doors. For the record, it is a lot easier to install flanged windows and doors than unflanged windows and doors.
So much so that there are kits marketed and sold that add flanges to unflanged windows and doors. A bit of history explains why. Commercial and institutional buildings were, until recently, masonry mass construction and residential construction has been by and large wood frame. Masonry mass wall construction required through-wall flashing at punched openings — the flashing had to extend from the interior lining all the way to the exterior face of the cladding. Whereas with wood frame construction the flashing only needed to integrate with the building paper layer behind the cladding.
Here is the key point. Both the brick layer and the block back-up were laid simultaneously. With both layers going up at the same time it was not possible to install a water control layer on the exterior of the block back-up wall Figure 1.
Penetrating rainwater typically ran down the back face of the brick layer not on the outer face of the block back-up wall. Through-wall flashing was typically located at the bottom of the walls. Note that it was a bad idea to drain the openings into the cavity airspace.
The result of this necessary use of through-wall flashings made it impractical to use flanged windows and doors at punched openings. In residential frame construction, building papers were common on the exterior of sheathings — between the sheathings and claddings. Because of this it was not necessary to drain the punched openings to the face of the claddings or veneers. The punched openings could be drained to the exterior face of the building papers.
Flashings were dramatically simplified as a result in residential construction compared to those in commercial and institutional buildings - and ultimately integrated with the windows and doors themselves.
Flanged windows and doors became common. Today, in commercial and institutional construction, we typically use frame construction — steel studs and gypsum sheathing are common — and we have water and air control layers installed directly over the sheathings or integral with the sheathings as in residential construction. As such it is not necessary to drain the punched openings to the exterior face of the claddings or veneers and it is possible to use flanged windows and doors.
Things can be simplified. Flanges should rule. Alas, it is not so. Tradition still rules and will likely continue to do so for the foreseeable future. Unflanged windows and doors will continue to be stalwart in commercial and institutional construction. So how do we make things work with unflanged windows and doors? We use the same fundamental approach that is used with flanged windows and doors.
The same physics apply. All the claddings are back ventilated and drained. Let me repeat. The exterior sheathing is typically exterior gypsum board but can also be oriented strand board OSB or plywood.
Note the exterior and interior sealant joints. Also note that the exterior sealant joint is weeped at the bottom of the window opening. And note the back dam. There should always be a back dam. Let me repeat…there should always be a back dam.
One provides a critical function from a water management perspective and the other is typically aesthetic providing closure to the bottom of the cladding system. The fluid seal could also be replaced with a membrane flashing tape.
Also note that the mechanically-attached water and air control layer extends over the top of head flashing and seal. In complex punched opening geometries fluid-applied flashings rule. In this sequence note that the self-adhered membrane flashing tape at the window head extends into the opening and that the head flashing is installed over this membrane strip.
This reduces air leakage at the head as the mechanically-attached water and air control layer is not sealed at the head. The plywood lining extends outward to line up flush with the exterior surface of the continuous insulation. In this sequence of details a fluid-applied water and air control layer is installed over the exterior sheathing. He loved that job. I grew up with a machine shop in the garage.
I am a second-generation engineer…and immigrant…somehow it seems important to point that out…. Two that are a big deal and one that is aesthetic. Let me repeat…there are three sealant joints….
Skip to main content. Joseph Lstiburek. April 16, Hence through-wall flashing was necessary at punched openings to drain the openings to the exterior face of the veneer. It was a bad idea to drain the openings into the cavity airspace. The use of through-wall flashings made it impractical to used flanged windows and doors at punched openings.
This mechanically-attached water and air control layer should not be sealed at its bottom edge at the head of the window to allow incidental water that penetrates the mechanically attached water and air control layer to drain out at the head.
Figure 5a, 5b and 5c: Self-Adhered Membrane Rough Opening Flashing Lining Coupled with Mechanically-Attached Water and Air Control Layer - In this sequence note that the self-adhered membrane flashing tape at the window head extends into the opening and that the head flashing is installed over this membrane strip. Upcoming Events Building Science Fundamentals. Renovation and Rehabilitation. Download
Window flashing in block openings.
Abstract: Integrating sill pan window flashing can be challenging using block-frame windows or installing flashings within a recessed opening in a concrete wall. Two case studies summarize the details of design and retrofit installation for sill pan flashing of replacement block-frame window into the perimeters of existing recessed concrete wall openings. Provisions for sill pan drainage were included with technical solutions for two case studies.
The design and detailing were also conceived to account for blending with the context of the existing architecture and minimizing the aesthetic concerns for the appearance of any exposed perimeter opening flashings.
These case studies demonstrate detailing methodologies for wood and metal block-frame window frames and concrete wall openings applicable for new and existing exterior wall systems. Skip to main content. Sill pan flashing for block-frame windows in recessed concrete openings-case studies. March 30, Author s : Robert Bateman. Services: Building Enclosure Rehabilitation. Keywords: Concrete Masonry Windows Wood.