Construction

How to Attach a Patio Roof to an Existing House

cbroderick — Thu, 16 Mar 2023 14:25:45 +0000

How to Attach a Patio Roof to an Existing House

cbroderick Thu, 03/16/2023 - 09:25

A bare, uncovered patio facing west will often feel exposed and uncomfortable, especially during sunny afternoons. That’s the case designer-builder Peter Brown faced at the Cook residence in Bozeman, Mont., and documented in his video, for which this article is derived. The homeowners asked Brown to design and build a roof for the exposed patio, which sits outside the dining room, so he set about considering the options.

[1] With a ledger and a 2/12 roof pitch, the bottom edge of the new beam was about 6’10”, or about 16” lower than the upper edge of the patio door.

The Design Process

As the first and probably easiest option, Brown considered installing a ledger under the eave for a simple shed-roof structure. He determined that doing so would limit the sightlines from inside the house.

“A cross-section view of this option shows that the combination of a low ledger height, minimal roof slope, and the depth of the supporting beam will block the views from the dining area,” Brown explains. [1]

From exploring the options in the cross-section views, Brown determined that, “A better option will be to use the supporting post and beam structure but work backwards from a beam height that preserves the view.” [2]

[2] Raising the beam and the patio roof preserves the view from the dining area.

“Again, this is illustrated in a cross-section view,” he says. “We first calculated a sight-line clearance height. Then going with a beam depth of 8 inches, a roof pitch of 3/12 and a 2x6 roof structure, we were able to determine the contact and bearing points of this new roof onto the existing roof.”

The existing roof—the eave specifically—is obviously the tricky point. The aesthetics are subjective, but Brown and the homeowners agreed on removing it underneath the new roof. That decision necessitated extending the wall plane up to the new 1x6 roof decking, while also closing in the cut-off eave ends in a tidy fashion. [3]

In addition, the home’s existing 6/12 roof uses trusses, so Brown needed to determine if and how he could cut them off. “We were able to contact the original truss manufacturer in order to verify that removing the eave area would not compromise the structural integrity of the existing trusses,” he notes.

[3] Cutting off the eave flush with the wall plane was an aesthetic choice and required a call to the truss manufacturer.

Materials For a Sturdy, Rough-Hewn Look

At that point, with the design finalized, Brown worked with the Cooks to decide on materials.

“It’s safe to say that this new structure will be the prominent architectural feature on that side of the home,” he notes. “With that in mind, we decided to go with a sturdy rough-hewn look. A typical exterior porch construction would be 4-by or 6-by post and beams. We decided to up the ante and go with 8x8 rough-sawn posts and beams, and 2x6 rough-sawn rafters.”

He also specified rough-sawn 1x6 material for the decking, topped with black roofing felt to block the view of the OSB from below, then the ⅝” OSB, and then matching asphalt shingles.Finally, as both a decorative touch and structural requirement, Brown specified custom chunky black steel pieces for the post-beam connectors and for the post bases/brackets.

Step-By-Step Installation

The construction process began with using a power plane to chamfer the edges of all the new rough-sawn lumber. “This extra step will add a simple but elegant touch to the overall finished product,” Brown explains.

[4] Post bases were custom fabricated for the 8x8” posts.

Following that is laying out all the 1x6 decking, 2x6 rafters, and 8x8 posts and beam for pre-staining with a nice-looking medium-brown stain.

The post brackets Brown specified are next up for layout and installation. “The use of 8x8 posts and beam required that we weld our own custom brackets and connectors,” he explains. “The two brackets to connect the post to the patio slab consist of 8-inch plate with vertical fins. These plates are attached to the slab with two 5/8x6” concrete anchors. Each vertical post is cut to length, secured to the brackets with lag bolts, and braced into a plumb position,” Brown notes. [4]

[5] The beam’s 15° chamfer provides the bearing surface for the rafters.

With the posts in place, the horizontal beam gets a 15° chamfer at the bearing point for the rafters. Then it’s hoisted into place and temporarily secured to the posts. [5]

Now that the beam in place, the two outside rafters are placed and squared into position. [6]

[6] The two outside rafters are squared into place to provide reference for the rest of the roof, including where to start cutting.

With the rafters in place, the crew can see exactly how much of the shingles, decking, and eave to remove, in addition to where the new components will be attached. [7]

[7] Cutting off the trusses required a call to the truss manufacturer for instructions.

“Once the eave is trimmed back and the exact bearing point location for the rafters is determined, a continuous 2x6 is attached across the existing roof surface,” Brown explains. [8]

[8] The new 2x6 provides a bearing surface and attachment point for the new rafters. Note the open eave, which will be closed later.

Each new 2x6 rafter is precut, seated on a 14-inch layout over the 2x6, and attached with an 8-inch structural screw. Blocking is attached to the low side of the 2x6, leaving a small gap at the top for ventilation. [9] It will get screened later. The blocking gives the wall below a clean termination point, as shown in the diagram. [10]

[9] The rafters are installed on 14” centers, not on the 24” truss spacing.

[10] The blocking is set to provide a clean termination for the wall below, as well as a gap at the top for ventilation.

Down at the eave end of the new patio roof, the rafters bear on the chamfered area of the beam. They attach through the top of each rafter with a 10-inch structural screw. Blocking between the rafters provides a more finished appearance. [11]

[11] A 10” structural screw secures each rafter at the chamfered surface. Blocking makes for a tidy look.

Atop the rough-sawn rafters, the pre–stained, rough-sawn 1x6 is attached with ¼” spacing. [12] Next up is the roofing felt, then ⅝” OSB, and asphalt shingles to match the existing shingles on the house. [13]

[12] Like the rough-sawn rafters, the rough-sawn 1x6 decking is visible from below.

As mentioned earlier, the upper part of the new roof has an area that could be an enclosed, unventilated dead space between the rafters. “Unventilated roof spaces can be trouble. So as a precaution, we have set the blocking low and installed 1/8 inch screening,” Brown notes.

[13] The OSB isn’t needed for strength, but ensures that shingle nails don’t show through the finished surface below.

Much like the decision to cut off the eave, how to finish off the cut ends is a mostly aesthetic decision. As Brown explains, “An area of concern during the design process was how to finish the areas where we removed the eaves. The eave terminations and wall area are very visible. We experimented with some mock ups and came up with a clean final finishing detail that blends well with the existing eave.” [14]

[14] The new eave terminations are clean and tidy, and are well protected from weather under the new patio roof.

The post-to-beam junction requires a connector, and while it’s possible to buy a variety of different pieces off the rack, custom pieces are fun to design and to make. That’s the approach Brown took for the Cook’s project. It was also a way to match the approach he took with the post brackets.

“One of the last details before roofing the new structure is adding permanent post and beam connections,” he explains. “As an artistic flair we had 3/16” plate sheared into triangle shapes drilled and finished. These simple connection plates add an interesting and functional finished detail.” [15]

[15] Simple and functional like the heavy rough-sawn lumber, these connection plates are spot on for this patio.

With the patio roof finished, the wisdom of this more-ambitious design is clear. Simply attaching a ledger would have been quick and easy in comparison, but also a bit flat and boring. “Mike and Gina are very pleased with the final product. This covered patio area greatly increases the livability of their backyard,” Brown notes.

Steve Hansen is a Colorado-based writer with a focus on the built environment—architecture, construction, renewable energy, and transportation. He can be reached at LinkedIn.

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A graceful integration may mean more work but improved functionality and aesthetics

Steve Hansen

Construction

Construction Practices

Jobsite Know-How

How To Improve Energy Performance in Existing Attics

cbroderick — Thu, 08 Dec 2022 14:32:11 +0000

How To Improve Energy Performance in Existing Attics

cbroderick Thu, 12/08/2022 - 08:32

I have been doing energy audits for more than 10 years now. I really enjoy studying building science and solving problems for customers. The only issue is that the jobs are typically in the attic or basement—two miserable and difficult places to work.

When tightening an existing house, one of the first areas to improve is the ceiling plane along the thermal boundary. Cathedral ceilings are typically not accessible from above, so flat ceilings with vented attics above are where the work is located.

On paper, a drawing of a roof/wall ventilation scheme is easy to understand and looks easy to install, but in practice, it’s anything but. Working under a steeply-pitched roof is bad enough [1], but a low pitch is worse.

Lying on rips of plywood placed across ceiling joists and reaching deep into birdsmouth cavities to fish around for fibrous insulation—which is often pushing against your face, arms, and shoulders—is no picnic. It’s often hot and always dusty. Even in cold weather, you will be covered with sweat.

Often the project involves tightening the ceiling and finishes with extra insulation—not necessarily because the existing R-value is too low, but because the quality of the installation is poor [2]. This can be because the contractor was paid by the square foot, which I know from experience leads to higher production but lower quality. It can also be due to the many things that can get in the way and complicate the job: AC units and air handlers; water heaters; ducts, wires, and pipes.

Pretty soon, there may simply be too many obstacles to properly sealing the attic at the floor. In such cases, it may be worth thinking about turning the attic into an unvented, conditioned space by spraying foam insulation into the rafter bays.

The R-value on the package of insulation is often compromised by the poor quality of the installation. Even if the original installation was properly done, older attics have probably had people crawling through them off and on for years. Many areas of the insulation will be packed down, torn up, or pulled out.

This gets complicated, given the many types of foam and the requirements of your climate zone, and is far beyond the scope of this article.

This is my general approach to making an unconditioned ventilated attic work best:

Air seal all penetrations and possible leakage paths
Insulate to at least the current energy code, not only to the proper R-value, but also to Grade I quality
Ventilate the attic at the rate of 1 sq. ft. per 300 sq. ft. of attic floor space, balanced at ridge and soffit areas

Sealing the Ceiling

Before I add insulation, I seal the attic. There are a lot of holes, gaps, and cracks that leak a lot of air. I make a sketch of the floor plan and include all penetrations that I can see from below. I orient this plan with the attic access hole so that when I am in the attic, I have a map to help me find everything that needs air sealing [3].

Some holes that leak air are obvious, like attic hatches or folding attic steps. Others are harder to find, like the continuous gaps along partition walls.

Gaps around light boxes, bath fans, recessed lights, wires, and vent pipes may be small, but they add up to a lot of leakage.

Venting Improvements

I start by assessing the existing ventilation. I look at the ridge vent both from the inside and the outside. The main problems I look for are a very low-profile ridge vent outside and inadequate roof sheathing cut away inside. Both of these conditions obstruct air movement.

I also take a close look at the soffit vents. The IRC calls for 1 sq. ft. of ventilation for every 300 sq. ft. of attic space, balanced between the ridge and soffits, but this is seldom the case in real life [4]. I have seen some older homes with soffit vents installed directly over solid wood soffits―they look like they’re vented, but they’re not. Even when soffit vents are properly installed, there may not be enough of them, or the rafter bays may be blocked by insulation, or the ventilation space along the ridge may not be sufficient.

Even when soffits are vented there may not be enough vented area or the rafter bays may be blocked with lumber or insulation. In some cases, non-perforated vinyl siding soffits have been installed over existing wood soffits, cutting off airflow.

Fixing these problems is not easy work. My company only addresses the work that can be done from inside the attic, with the occasional exception to tear out and replace some soffits. If a ridge vent needs to be installed or improved, I recommend hiring a roofing contractor. I typically work alone, but if there’s enough room in the attic for two people, one person can prepare and feed materials to a second person, who installs them. Given the low headroom at the eaves, this would reduce the number of times someone had to crawl in and out of position in a rafter bay.

Step-by-Step Process

I concentrate on improving the ventilation at the eaves, where the rafters sit on the exterior walls. I want to open up this pathway so air can easily flow in and push warm, moist attic air out of the ridge. I also want to prevent this air movement from washing over or through the attic insulation, which reduces its effectiveness. The plan is to create a solid barrier that provides a 1- or 2-inch path over the insulation and also seals the end of the insulated area where it meets the top plate of the exterior wall.

To clear a workspace in front of the rafter birdsmouth, I pull out the last 18 inches of existing insulation in the attic floor. Rather than folding it back to replace later, I cut away the excess and save it to install in some other area of the attic after I have finished sealing. The uninsulated area in the floor will be filled with loose cellulose or fiberglass insulation blown against the new baffles. This does a much better job of insulating than just pushing the old insulation back into place in this very critical area of the attic.

Next, I custom cut a piece of rigid foam to the right width, which can vary from bay to bay, especially in older houses. The “right width” is one that is not so loose that it doesn’t stay in place while I seal the edges with caulk or foam, or so tight that it can’t be pushed into place. I crosscut these from 4 x 8 sheets so that the pieces are 4 ft. long. I typically use foil-faced isocyanurate or XPS, depending on price.

To provide airflow, the rigid foam has to be spaced off the roof sheathing. If a rafter bay already has one of those thin, narrow foam baffles installed, I just leave it there and use it as the spacer [5]. Otherwise, I create stop blocks for the foam panels by ripping 1½-inch-wide strips of foam and gluing them to the rafters on each side of the opening.

To provide airflow from the soffit vents, the baffles need to be spaced away from the roof sheathing. Any thin foam baffles already installed are left in place to serve as spacers.

Otherwise, narrow strips of rigid foam are glued to the rafters to serve as spacers, and the foam panel is slid down into the rafter bay.

At the wall plate, the foam panel extends past the outside edge of the wall plate, and a narrow strip of foam cut from the top of the baffle is pressed into place from the attic side to serve as a draft stop. All edges and gaps are sealed with expanding foam to prevent air from blowing over or through the attic insulation.

After patching existing floor insulation, the final step is to add loose fill cellulose or fiberglass insulation on top.

With the spacers in place, I slide the foam panel between the rafters and push it down until it extends past the exterior edge of the wall plate. After measuring the vertical distance from the outside of the top plate to the bottom of the foam, I cut a strip of that width off the top end of the foam panel. Then I press this ripped piece (which may be as narrow as 3 inches) tightly into the cavity to close off the space where the insulation meets the outside of the wall.

Finally, I seal all the gaps along the edges of the foam panel, including the draft-stop at the wall plate. I use expanding foam because it easily fills in the larger gaps that I often have (hey, I’m a drywaller, not a furniture maker).

The foam panels open channels for air, but inadequate or blocked soffit vents will defeat their purpose. A good way to quickly see if there is an open path for air is to go into the attic during the day and shut off all lights. If you see light coming in above the foam baffles, then there is an open path. Very little light could mean that there are not enough vents in the soffit material or the vents are blocked. This may require retrofitting the soffit vents from the outside, which is beyond the scope of this article.

The process described above adds R-value, prevents wind washing, improves airflow, creates a dam to blow insulation against, and improves the performance of the insulation along the attic perimeter. I believe all these benefits make the struggle #WorthIt. After the ventilation, air sealing, and insulation work is done, the clients will save money on their energy bills, but that’s not how I sell it. What I sell is greatly reduced ice dam problems; no more moisture stains on ceilings or moldy attics.

Myron Ferguson is a drywall contractor whose many articles and links to instructional videos can be found on his website (ThisIsDrywall.com). In recent years, he has added home performance to his repertoire. This is an edited and updated version of the original article at ProTradeCraft.com.

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There’s more to insulating the attic than attic insulation; there’s venting, air sealing, and misery

Myron Ferguson

Construction

Construction Practices

Building Science

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November/December 2022

How to Install PVC Bevel Siding Over Rainscreen

cbroderick — Tue, 25 Oct 2022 17:27:49 +0000

How to Install PVC Bevel Siding Over Rainscreen

cbroderick Tue, 10/25/2022 - 12:27

In 2021 (How to Build a Rainscreen for Open-Joint Cladding and How to Install Siding That Lasts), we wrote about new rainscreen materials and open-joint PVC siding. The project was part of what was then a new video series at ProTradeCraft.com about construction in extreme climates, called “Building Resilience.”

In this article, we look at siding again, but this time it’s from episode 10 of the second season of Building Resilience. The project is a remodel of beautiful home built in 1904 that is also the international headquarters of OA Design + Build + Architecture in Minneapolis, an extreme climate indeed.

In this next-to-last episode 10, the exterior walls have been prepped for siding using a variety of products from Benjamin Obdyke, all of which are covered in more detail in earlier episodes [1].

The water-resistive barrier (WRB) is self-adhered Hydrogap SA, with seams sealed using HydroFlash GP Self-Adhered Flashing tape (episode 6), followed by a layer of Slicker Max, which creates the ventilated rainscreen (episode 7).

Wall penetrations are flashed with liquid-applied Hydroflash LA (episode 7), which OA Founder Michael Anschel likes to use because, as he puts it, “you know, old house, weird pieces of wood, things coming together.”

The project includes areas clad in open-joint boards, which provide a contemporary detail, but most of the building will be clad in beveled siding, partly, as OA Founder Michael Anschel explains, “to pay homage to the period it was built,” but also to have a go with a new PVC beveled siding product from AZEK [2].

Anschel notes that it looks just like smooth cedar, then asks a question you’re probably asking: “If you’re trying to make it look like smooth cedar, why not just use smooth cedar?” To answer, he points to rotted trim boards and peeling paint on the wood-clad building next door. “All of the challenges that come with wood, which is a great material and it’s beautiful, but let’s face it,” Anschel explains, “when it comes to our cladding, something that is really, really weather-resistant is probably our best bet.”

Anschel holds a scrap of the new PVC beveled siding product from AZEK in which most of the building is clad. The material is virtually impervious to decay from exposure to moisture, and as with other PVC products, can be easily worked with wood-working tools.

Step-By-Step Installation

Installing PVC beveled siding is just like installing wood beveled siding, with one important difference: PVC expands and contracts differently from wood―and for different reasons.

(To learn more about how it behaves, why it behaves that way, and what you should―and shouldn’t―do to avoid problems, see “Understanding How PVC Trim Moves")

Fastening is important to control movement in PVC, so the first step is to mark lines on the Slicker Max to locate the studs [3].

Marking stud locations on the rainscreen helps ensure alignment of the fasteners, which will be exposed.

Fastening the PVC siding through the rainscreen to the framing also helps prevent movement. To promote drainage, a temporary spacer block holds both the 1½-inch-wide starter strip and the first course of siding ¼ inch off the metal flashing.

The crew adjust for level before nailing both pieces in place.

Next is to use a 1½-inch-wide piece ripped from the top of a siding board as a starter strip, which will properly align the bottom of the first course of siding. The two-man crew uses a block to hold both pieces ¼ inch off the metal flashing, and rather than tack the starter strip first then nail the first course of siding, they fasten both pieces at the same time.

The nails, which will be exposed, are placed about 5/8-inch up from the bottom of the board, one nail per stud and no closer than 2 inches from each end.

The crew used two sets of spacer blocks to keep the courses even. One set are simple 4-inch squares used only to set the second course because the wider skirt board doesn’t leave enough room to hook a spacer under the first course. The main set are cut from heavier PVC stock into an L-shape, with one 4-inch leg, which is the amount of reveal they are looking for, and a short ½-inch leg, which hooks under the course below [4].

After setting a 4-inch reveal with the second course, the crew uses a set of L-shaped blocks that hook under the course below. They serve a dual purpose: they ensure a uniform reveal and they provide a straight edge that makes it easy to square up from the nails below, ensuring a straight line of exposed fasteners. Metal butt flashing behind the joints directs any water out before it can get behind the siding.

As with wood siding, it can get tricky at penetrations, particularly profiled head casings at windows and doors. But the tools you use to work wood―power saws, coping saws, multi-tools, even sharp chisels―also work with PVC. But there is no grain, so boards with deep cutouts can be floppy, and longer lengths may require two people to maneuver into position on the wall.

After that, it’s rinse and repeat around the rest of the building.

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It’s a lot like installing wood bevel siding, except it won’t warp or rot. And it expands and contracts differently and for different reasons

Sal Alfano

Construction

Construction Practices

Jobsite Know-How

September/October 2022

Understanding How PVC Trim Moves

cbroderick — Tue, 25 Oct 2022 16:24:45 +0000

Understanding How PVC Trim Moves

cbroderick Tue, 10/25/2022 - 11:24

In “Shrinkage: How PVC Trim Moves,” an installment in ProTradeCraft.com’s building science audio series “7 Minutes of BS,” David Parker, director of exterior applications with AZEK Building Products, explains that PVC and wood move for different reasons: “PVC moves thermally, whereas a wood-based product moves with moisture. So, wood-based products typically swell, and they swell within their width and a little bit in their length. The difference with PVC is that PVC does not swell or move in its width, it expands and contracts with its length.”

The problem with PVC trim installs is that builders and remodelers who try to allow for that movement get it wrong, even though they’re trying to do it right.

“What people typically run into with PVC,” Parker says, “is that they install it with gaps.” This seems to make sense because, unless it’s a ridiculously hot day, the PVC will expand in the summer and shrink back down in the winter. “That the first season, it does exactly that,” Parker says. “It expands and they may have very few gaps at the ends of their boards that summer, and then that next winter it contracts, as would be expected with PVC—and most building products, for that matter.”

The surprise comes the second summer, when the PVC never comes back to full length again.

What happened?

“As with any plastic that goes through a heat cycle,” Parker explains, "there are fibers within the PVC product that relax, and that relaxation … causes it to shrink slightly.” It will expand again as the temperature rises, but after that first year it will always shrink back to a smaller length than it was when it was installed.

So What Now?

The first part of the solution is proper installation.

“One of the misconceptions is that for every 18 feet, you need a ⅛-inch gap at the ends when it’s cold outside,” Parker says. “We actually don’t want you to do that.” Instead, plan for the fact that the piece of PVC you are working may eventually end up a bit shorter than it is the day you install it. The key is proper fastening, proper treatment of field joints, and allowing for gaps at the ends of boards.

With PVC skirt boards, for example, gluing the scarf joints and driving fasteners on both sides will prevent a gap from opening up in that initial expansion-contraction cycle. The fasteners will keep the board from buckling as it expands, and the boards will stay tightly joined when they “relax.”

At the ends, use a detail that allows for some movement; ideally, it would also hide any gaps that develop or at least render them inconspicuous. Or with a rainscreen system, plan for a small seasonal gap, which may look better than a caulked joint.

Pay Attention to the Paint for PVC Trim

The second part of the solution has to do with painting PVC. Dark colors absorb more heat than light colors, which causes more heat build up. “The higher the heat-build, the more shrinkage you could have down the road,” Parker says.

Can you paint PVC trim? Yes, but pay attention to the LRV or Light Reflectance Value of the paint. As the name implies, it’s a measure of how much sunlight―and, therefore, heat―a particular paint color reflects. You can usually find it on paint chips or color swatches on the paint manufacturer’s website.

“As long as that LRV is above 55,” Parker says, “with 100% acrylic latex paint, you’re good to go, and you won’t get excessive heat build.” For lighter colors with LRV above 55, you can use standard high-quality acrylic latex exterior paint.

It’s still possible to use very dark colors, but you need to use paint specially formulated with heat-reflective or solar-reflective technologies. Parker notes that many manufacturers have a “vinyl-safe color palette” that has been tested and measured for heat-build.