Continuous interior to exterior beam
All;
I have a client that wants to design a home in Dallas, TX with a post & beam look ala Joe Eichler – exposed interior to exterior ceiling beams – I have attached some mockup pics. Don’t know yet if those are going to be structural or not – but either way, I can see some issues with several large 16″ beams continuing from interior to exterior. What are your thoughts on such a design, has anybody done something similar before and what was your experience with the performance of such a design – any particular detailing…
Thx for any input. Of course, if the beams are non-structural, they could be broken at the exterior wall points so there would be no penetration of the exterior wall assembly, but I can see lot’s of headaches with that method too. As always any thoughts and input is appreciated.
Marc Kleinmann
Dallas, TX
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Replies
Marc
Does the building have a flat ceiling as shown? I do a lot of homes with exposed rafter tails, 6"x8".
Allan
Marc,
Many Architectural styles have built that way for centuries, and the deeper the overhang the more protected would be to the weather; however, thermal bridging would occur. What I have done in the past is to stop the beams or timber trusses at the outside edge of the wall, install rigid foam board outside of the wall sheathing and cladding, and then continue with the faux beam outside. It’ll help you with the thermal bridging at the beams, it solves the moisture intrusion and you will have a better insulated wall overall.
A second option if you don’t want to use exterior foam board could be to stop the beam or timber truss 2” from the outside edge of the wall, cut out 2” rigid foam to fit, then finish your wall and install the faux beams outside.
A third option would be to install a 2” rigid foam band all around under your Soffits and trim with cladding, and then install the faux beams.
As you can see, the object is to break the continuous beam to avoid thermal bridging and moisture intrusion.
Allan - yes flat ceiling following roof line.
Armando - Exactly my thoughts. Been thinking about "breaking" the beam at exterior wall but have one concern about this... at a 3' overhang and a solid 16" beam... what about the weight of these attached to roof structure?
How much does overhang extend past the building?
Marc,
Install a couple of nailers between the rafters, glue the beams to the soffit and use long screws or toe-screw them all the way through the nailers.
Make sure your "flat" roof has a 1/4"-1/2" slope minimum. Depending on the aesthetics and style, you may need to install parapets, crickets and drainage system.
I guess if it’s too heavy of a 16" beam, you may need to drill through the middle of the corbel/beam and bolt them to a nut & washer above the nailers; and then you may want to “plug” the bottom for aesthetics. A lot of work, but if that’s what you client wants…
Allan - 36" overhang
I think John is correct about spacing.
Marc,
I think you should look more carefully at the Eichler Designs.
It looks like your "beams" are spaced too closely together...
Yours seem to be about 48" inches OC
The beams in the Eichler Houses are more like 80" or sometimes 96" OC
The beauty of the Eichler designs is that the materials are used in a judicious way.
I think it would be a "Faux Pas" to strap on Faux Beams.
http://sunnyvale.ca.gov/LinkClick.aspx?fileticket=UefnSct7JT4=&tabid=478
John;
You are correct about the spacing - most of the Eichler designs were based on a 84" & 96" oc spacing - my mockup pic was solely posted as an example of the construction method an not as a design intend. Obviously, on elevations that have full glazing the "faux" beam is not an option anyway. I'm talking mainly about areas that have some glazing between the beam spaces and brick/siding underneath. For these areas, would it be worth the trouble of "breaking" the beams to eliminate thermal bridging in these areas?
I guess I'm looking for opinions on how "efficient" a design like this could be.
Thx,
Marc
With beams at such a large spacing, it would seem to me if a good sealing system could be developed that the relatively small square footage of a moderate insulator[wood] the gain would be very small in a fairly complex detail .
I have 28 such penetrations in my house, and assuming they were sealed perfectly I cannot see a gain of more than about 80 btu/hr at 70 degree delta.
I can think of structural reasons why the continuous beam is superior, especially with big overhangs
Marc,
Beauty is an idiosyncratic concept. But to me, homes with major thermal bridges are aesthetically disturbing. Looking at them hurts.
But many architects have a different sensibility, I guess.Traditionally, most U.S. architecture schools have been weak on building science education, and these types of painful designs are one result.
Ahh, the things we do for beauty...... the picture in post 10 is the 6 inch heel of the architectural world......the beams would not seem to be the biggest source of heatloss by a long stretch. The contortions needed to eliminate them[and keep the look] would seem unwieldy.
Martin,
I agree with you about Architecture Schools and Architecture Media.
Overglazing, Cantilevers, "expression of structure" and "the continuation of inside to outside"...
These things are still encouraged in the Architecture schools and glorified in Periodicals(Fine Home Building included) and AIA Awards.
This type of "fashion" is certainly Not-So-Energy Efficient.... And not what I would recommend.
(unless I lived in San Diego or Bali)
In Marc's case I would be more concerned about the Eichler overglazing penalty.
I plead guilty to finding the fashion/style attractive.
ahh...apparently quite a bit of wood was rejected for bill gates house, john. it's certainly some of the more interesting framing i've seen- and for $800+/sf, i would expect it.
unfortunately the decaying concrete wall totally ruins the effect.
My practice has been faced with attempting to upgrade the thermal performance of a number of these Eichler-style relicts from the days of cheap oil. And yes, the thermal bridge is typically the least of one's worries: the over-glazing and the frequent absence of ANY roof insulation other than the 2" thick t & g roof deck are far more consequential. The design esthetic stems from the common misapprehension that the best way to integrate interior and exterior spaces is to separate them only by a thin glass curtain wall. It's past time to get beyond such naivete and thoughtlessness.
Glass Sells!
I think Taunton (Fine Home Building) is as guilty as the rest of the profession/industry/media that promotes glass, glass & more glass
I am perfectly happy and comfortable in my home with Not-so-much glass and not-so-high energy bills
I would seriously consider giving the folks at Faux Wood Beams a call - they're really knowledgeable and could help you figure out what would be best for this project...if you're interested in using a faux alternative for the beams/rafter tails.
FWB Contact page
Hi Marc,
Yes, your client can do exactly what they want to do - design and build an extremely efficient home that follows Joseph Eichler's designs.
We are undertaking a renovation and new construction of our Eichler home, which was designed by Claude Oakland and built in 1969. We are renovating the ground floor of the home and adding a complete lower level (basement) through new construction.
We reduced the number of structural beams penetrating the exterior front/rear of the house from 8 to 6. At the same time, we covered the atrium and used R-47 SIPs on the flat roofs and gable roofs. The flat roofs were covered with polyiso tapered foam, averaging 3 inches, with a white TPO to reduce the solar gain. The gable roofs were covered with yellow cedar shakes, with a high albedo (and durability) to reduce solar gain, as compared to red cedar shakes. On the East/West walls, we cut the beams in two and added 2 inches of foams to make insulated headers, which reduces the thermal bridging.
The house utilizes a ground source heat pump (geothermal heat exchange) through a 2,800 ft ground loop. As well, there will be 48 215-watt photovoltaic panels on the roof to generate electricity.
In constructing the lower level (basement) under the existing house, we added 1.5 million lbs of concrete. All of the concrete was insulated to at least R-10 so we have a huge amount of insulated thermal mass. The existing exterior walls were increased from 4x to 6x and the resulting structure exceeds (is better than) California's Title 24 by 72.9% (and the California Energy Commission verified the calculations through the Energy Pro model).
The windows and sliding glass doors are all high performance, by Fleetwood. In fact, we have a 24 ft sliding glass door, made up of three panels. All of the gables have clerestory windows and the flat roof over the atrium has clerestory windows on all four sides. We designed the overhangs to minimize the solar gain during the summer while taking advantage of the solar gains during the winter.
While there may be higher energy costs with glass, there are also energy savings on the lighting side. We are bringing a tremendous amount of natural light into the lower level (basement), which is over 24 ft from finished floor to finished ceiling.
Our plans and other information are on our 'construction blog', at http://www.EichlerVision.com.
Bryan,
Your basement has 1.5 million lbs. of concrete?
Since concrete has a density of 145 lbs/cu. ft., 1,500,000 lbs. of concrete = 10,345 cubic feet = 1,149 cubic yards = 128 truckloads of ready-mix.
[Later edit: the above calculations include an error, as Keith Gustafson pointed out.
10,345 cubic feet actually equals 383 cubic yards. Sorry.]
Methinks both of yuze math is off.
I get 383 yards, still a bunch
10345 cubic ft /27 =383
His blog is a bit dense, but there just might be close to 400 yards of concrete there, buncha work
Oops! Thanks for catching my error. That's still 43 ready-mix trucks.
Hey I am a bit of a nut precisely because I screw up math so often
I haven't got the time to dig thru his blog, but I think I see that it has a 14" plus 4" pour in their somewhere, and the house is like 54 foot square......
Yes, there is a lot of concrete in the structure. The foundation is sitting on a 'seasonal perched water table' and we have water 5 ft below grade at certain times during the year (i.e., at the end of the rainy season). Over the course of the year, the water level drops to 15 ft below grade (or so)..
Since we excavated 13 ft, we have to displace 8 ft of water. The house is 54 ft 1 inch by 56 ft 4 inches, or 3,047 sq ft. Water is 62.4 lbs/cubic ft and we displace 8 ft, so each sq ft is 499.2 lbs.
To simplify the math, we have 3,000 sq ft x 500 lbs/sq ft, or 1.5 million lbs. Our building challenge was to make a concrete boat that sinks. And, as that boat sinks, it much be so strong that it does not break or crack.
The initial reaction of the structural engineer was to have us put in a 36 inch slab. Instead, we used 6 inch hollow core concrete panels that were covered with at least 3 inches of concrete and we were able to reduce the basement slab to 18 inches. But we went with 20 inches to make everyone comfortable that the house wouldn't float.
All of the concrete is insulated, so the mass helps with maintaining a stable temperature. In Northern California, we have two seasons - day time and night time. The slab is slow to heat up during the day, and slow to cool down at night.
I thought it was summer, fire rain, mud..............
Oh, maybe that is SoCal
Your blog is kind of hard to 'get'. A loottttt of details but hard to navigate, figure out what is going on, or maybe I'm dense.
The floating part did not jump out, but yeah, floating would be bad.
One way that we have tried to increase the thermal performance of a post and beam houses on the south coast of B.C is to detail the beams assuming that they are going to be strapped, insulated and clad with (wood) siding.
We have designed and detailed structural systems using cantilevered beams that are treated in this manner so that you get the benefits of the structural system while minimizing the thermal bridging.
It was not uncommon here on the south coast of B.C. for beams, be they glulam or sawn timbers, to have been clad with cedar siding (of varying grades depending on budget and appearance) on the interior faces. Taking that one step farther, you can strap then clad the beams on both the interior and exterior (cantilevered portion). The exterior strapping can provide space for some form of insulation. By designing for a thinner structural element (beam) that you can strap, insulate on the exterior and clad you to get that continuous beam and mitigate somewhat the thermal bridging. The result is a highly desirable Form that Functions well and provides the occupants with the Delight that we are all trying to achieve.
I would actually be more concerned about the roof insulation and the glazing system.
These houses usually have no attic space and the ceilings are often exposed structural wood decking. To add insult to injury the windows were most often single-glazed and usually 'site glazed' using simple wood stops - not premanufactured and tested windows. With today's sophisticated thermal glazing systems it is not that difficult to achieve the 'post-and-beam' form without dismal thermal performance.
Contrary to some of the previous comments I would personally go for the Eichler form using modern construction detailing and techniques.
Good Luck with it!
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