Banish These Details From Your Plans
Some features and methods are so difficult to implement that designers might want to avoid them entirely
Is it possible to disassemble old shipping pallets and glue the pieces of lumber together to make furniture? Of course it’s possible; some woodworkers have used this method to make beautiful tables and chairs. There’s a fly in the ointment, however: while it’s possible, it’s not very easy.
Many commonly used construction methods, design details, and materials fall into a category I would call “possible but not easy.” I decided to create a list of items that fall into this category.
The unfortunate twist to this category of difficult methods is an apparent paradox: though hard to do well, these methods are actually fairly easy to implement if you are willing to do a sloppy job. (That’s why many of the methods are common.) The methods are only difficult for builders who want to build a tight, high-performance home.
My list is deliberately provocative. Some readers will respond, “I’ve used many of the methods on your list, and I always do a good job.” To which I will answer, “That’s great. But most builders aren’t as conscientious as you are.”
I’m addressing this article to architects and designers. Since these methods are hard to implement well, it’s best to leave them off your plans and specifications. Use other methods.
Martin’s ‘possible but not easy’ list
Look your client in the eye and just say no. It may take a little practice, but you can do it.
Crawl spaces. Most crawl spaces are damp, leaky, poorly insulated, and rarely visited. Creating a dry crawl space is possible, but it’s rare for a builder to get all the necessary details right.
Basements can be damp, too — but at least they are easier to access. (Easy-to-access spaces are more likely to be frequently visited, and frequently visited spaces are less likely to have problems that go unnoticed for years.)
Slab foundations have drawbacks — but nowhere near as many pitfalls as crawl spaces.
For more information on this issue, see Building an Unvented Crawl Space.
Dormers. Occasionally, an architect will design a dormer for a vented unconditioned attic, in hopes of creating a roof that looks lively and exciting from the curb. (Needless to say, this is nuts. It’s the kind of detail you would see on a Hollywood set.)
In most cases, however, dormers are specified when the space under the roof is conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. . The components of this type of dormer are part of the home’s thermal envelope, and it’s hard to get the details right. The thermal envelope has to be continuous. That means that you need to have insulation that follows the roof slope; when you pop a dormer, you need to make sure that all of the barriers — the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., the water management barrier, and the insulation barrier — are uninterrupted, and that the barriers on the dormer cheeks are continuous with these barriers on the main roof.
Let’s face it — the air barrier ends up like Swiss cheese. Moreover, the framing used for dormer cheeks and dormer rafters is never thick enough for an adequate insulation layer, and the roofer’s step flashing details at the base of the dormer cheeks are often faulty.
So — don’t do dormers.
Bay windows. Bay windows are almost as difficult to detail well as dormers. In most homes, this type of bump-out is an energy nose-bleed.
If you insist on building a bay window, make sure that you have developed good details to limit air leakage and to provide a thick layer of insulation.
Garrison overhangs. The second floor of a Garrison-style home has a greater area than the first floor. This magic is made possible by cantilevering the floor joists a foot or more, creating an exterior soffit.
You can guess what’s coming: I don’t like Garrison overhangs. These bump-outs are hard to seal, so they usually leak abundant quantities of air.
Windows in showers. You want a window in your shower, don’t you? Maybe you live in the country. You don’t have neighbors, and you enjoy the little frisson of excitement you feel when you shower in front of your window. Or maybe you just want to look at the trees or enjoy the natural light.
Can you install a window in a shower in a way that keeps water out of your wall? Sure. With enough copper flashing, butyl gaskets, and peel-and-stick tape, you can do almost anything. Do most window installers get these details right? No.
Fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. . Yes, it's possible to install fiberglass batt insulation in such a way that it achieves the R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. advertised on the package — but it doesn't happen often. If you care about the thermal performance of the building you are designing, it's best to specify a different type of insulation.
Recessed can lights in insulated ceilings. Many builders have tried and failed to make recessed can lights airtight, using a combination of caulk, spray foam, and site-built covers. They've also tried to heap enough insulation on top of the fixture to meet minimum code requirements, only to be stymied by insufficient clearance to the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. or difficulties keeping the mounded-up insulation in place.
Fortunately, most designers who focus on energy efficiency have sworn off recessed cans. The biggest remaining problem is that designers are weak; they need to develop a backbone to better resist homeowners who plead for recessed lighting.
Brick veneer. Brick claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. is durable, low-maintenance, and attractive. Traditionally, however, bricks were not intended as a facing for structural wood framing. The idea of marrying masonry cladding to structural wood framing is a relatively recent development, and it is fraught with problems.
How many ways are there to screw up brick veneer? Lots. The builder can use the wrong wall sheathing; the builder can install the water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material. (WRB) with reverse laps; the mason can forget the weep holes at the bottom of the wall; the mason can fail to install durable flashing near the weep holes; the weep holes can end up below grade after landscaping work is completed; the mason can fail to install proper flashing and weep holes above a bay window; and the mason can clog up the drainage space behind the bricks with gobs of mortar.
Is there a good way for the architect and builder to make sure that all of these details are done right? Not really — not without a webcam.
Including brick veneer on this list is something of a stretch, I know — and I'm going to get pushback on this issue, especially from builders in Texas and Georgia. But designers and builders who specify brick veneer need to be aware of the pitfalls of this cladding, and need to have a plan for supervising the work carefully.
Adhered manufactured stone cladding. Adhered manufactured stone cladding over OSB sheathing is probably the riskiest cladding option for a wood-framed building. Hundreds — perhaps thousands — of homes with this type of cladding have had serious problems with moisture intrusion and rot, dragging the homeowners, builders, designers, and their insurance companies into protracted construction-defect negotiations.
If a designer and builder can come up with details that include a ventilated rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap between the cladding and the OSB, along with bulletproof flashing details, this cladding option might work. If you want to go that route, you have a stronger stomach than I do.
For more information on this issue, see All About Wall Rot.
Ground-source heat pumps. There are two hurdles that need to be crossed if you want a residential ground-source heat pump (GSHP) that performs well: system design and equipment installation. Both are difficult. Energy experts have learned that both steps are often muffed.
For more information, see Air-Source or Ground-Source Heat Pump? and Are Affordable Ground-Source Heat Pumps On the Horizon?
Ducts. Most ducts are undersized. Most duct seams are leaky. Many ducts are convoluted and are located outside of a home’s thermal envelope. To overcome a duct system's static pressure, furnace fans and ventilation equipment must expend a significant amount of energy.
If you are designing a home, one solution to these problems is to choose systems (for example, ductless minisplits or Lunos ventilation fans) that don’t require ducts.
If you decide to install equipment that requires ducts, make sure that:
- The duct system is designed according to standard engineering principles;
- The ducts are installed as shown by the system designer;
- Duct seams are sealed with mastic or high-quality tape to make them as airtight as possible;
- All ducts are located inside the home’s conditioned envelope.
For more information on this topic, see:
Can all of these features be avoided?
It’s perfectly possible to build a house that has none of the features on this list. Such a house will be easier to build and will be more likely to perform well than a house that includes several of these features.
If you are an architect who wants to include some of the features on this list, my opinions are unlikely to dissuade you. Just make sure that you provide your builders with plenty of detail drawings. And it might be a good idea to stop by the job site frequently to make sure that everything is going according to plan.
What did I forget?
If you think I've left off a few important items from this list, feel free to set me straight in the comments section below. After all, adding to the list is fun.
So far, the suggested additions to the list include:
- Beams or joists that penetrate the thermal envelope.
- Obscenely complicated rooflines and ceiling height variations.
- Roofs with stingy overhangs.
- Cathedral ceilings.
- Glass that extends to the floor.
- Sliding doors.
- Decks over living spaces.
- Flat roofs.
The above bullet list includes the most defensible suggestions posted below by readers of this article. Although I have cataloged the suggestions as a public service, I am not ready to defend all of them. To learn more about the reasons why these items were proposed for inclusion on the list, read the comments below.
Martin Holladay’s previous blog: “How Balanced Ventilation Systems Become Exhaust-Only.”
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