Ridge beam placement in a clerestory roof
Hi all,
I’ve got a quick question about framing a clerestory roof. I am planning on using a ridge beam to support the roof load, to allow for cathedral ceilings. Looking at the roof, I can see two places where one could place a ridge beam:
a) Place the ridge beam where the ridge would be if the roof was a gable with no clerestory.
b) Treat the roof as two distinct shed-style roofs, with a ridge beam on the top and bottom points of the clerestory.
To make it clear what I mean, I have attached an illustration based on the roof design I am working with. The ridge beam is represented in red.
For both possible placements, I have been able to find example images where they appear to be used in a build — though just because it can be done either way doesn’t mean that it should be, and I am curious whether one placement is more sound than the other.
Project is still in the early drafting stages, and an engineer will be consulted before this all is through. I’d just like to have a good enough idea for now, as I like to keep the framing in mind as I draft.
Other build details, if they happen to be relevant:
-Roof slopes are 6:12 and 24:12. The steep slope is for solar panels; it is based on the angle of the winter sun at my latitude, and will ideally prevent snow from sticking/make clearing easy.
-Building is 24′ x 24′. Runs of roofs are 18′ and 6′ respectively, relative to clerestory. Runs are 16′ and 8′ relative to where the “ridge” would be on a gable.
Let me know if I can provide anything else to help, and thanks ahead of time for your answers
Edit: Attachment doesn’t seem to be working? Or maybe the redesign just has me confused.
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Replies
Aedi,
I vote to let an engineer design it.
Common sense tells us that both shed roofs need support at their peaks. If the beam at the peak of the lower roof is designed to carry both loads, the upper rafters can bear on the same beam. See photo below.
Another advantage to dropping it the way it was done in Martin's photo, is to keep the beam within the conditioned space, and avoid excessive thermal bridging.
Depending on the spans, the loads may end up too large for one beam. If that's the case I'd consider placing one where we have discussed, and the upper one a foot or so in from the wall.
A third alternative, which would only be possible if you don't have clerestory windows, would be to get your engineer to design the wall as a box beam,
Any of those approaches can work, depending on your goals. I've designed projects with the beam below, as Martin's photo shows, as I think it's the cleanest look, and as Malcolm said, it's better from a thermal standpoint. On one project there was a long span so we used a girder truss instead of a beam. But you need to make sure the upper ridge is braced against lateral movement, so you should involve an engineer.
Aedi,
I built my clerestory pretty much as Martin suggested. Two ridge beams, one bellow and one above. The one above is quite small as it only needs to span the distance between the windows, the same size as the rafters, hidden behind the drywall.
To make the window flashing details easier and to have larger glass, I moved the column supporting the upper ridge behind the windows (inside the conditioned space) and used a wider top and bottom plate. This meant that instead of having to install and detail 8 separate windows, the whole thing was just one long unit.
One item to watch for is for your overhang if it as south facing window. I undersized mine slightly and get a bit of solar gain near the tail end of the cooling season.
Good luck.
Thanks all for your responses!
Its good to see that it can go either way. I will be sure to have an engineer review all the plans, so you can all rest easy on that.
The consensus seems to be that having two ridge beams is the better choice, so that's what I will have in mind as I work on the design. The spans involved are rather small -- 24' of roof, somewhere between 10' and 14' clear opening, depending if I throw in another support column (part of my reason for wanting to know the optimal ridge placement, to see where this column would fall), so having the lower ridge support both loads should not pose a problem. Again, I'll be sure to get approval from an engineer :)
Thanks Akos for including those specific details in your post. I was considering whether it made sense to use an extra long window vs multiple smaller units, and the trade offs between easier flashing details vs. the potential for more insulation, depending on the gaps between them. And I'll be sure to play close attention to the overhangs.
I know this entry is now 3.5 years old but I have a similar issue and wonder how you resolved it.
My house is clerestory, or as this county calls it semi-monitor construction, the man who designed and built the house in 1991 is long deceased. He was an engineer at a nuclear power station near here, but when the county switched over from paper blueprints to microfiche, then later electronic records, my house plans were not among those they transferred to film.
I have no resources other than to contact and pay several thousands of dollars to another engineer just to find out what the technical details of the construction are. I know some basics from my time working in construction where an engineer took me under his wing and made the time to explain what the fundamental aspects of our project were. The math on loads and such just were not part of it.
I will state that it appears to me that he built this house - or should I say overbuilt it, much like his nuclear power plant. I am attaching his solution in a couple of photos that should address your question even though by now your project is long finished. Mine on the other hand revolves around the header beam one side of the roof rests upon, it has rotted in the Florida heat and humidity and now has to be replaced. The side that rests on that header is the high, larger side of the roof with rafters 24 feet long by 4X10 of cedar 6 feet on center apart. The other side, a shed roof that meets the higher wall with the windows is 4X10s 18 feet long with about 11 feet interior floor space. The rest is the exterior, and then inside extends so the short side rafters meet the long side rafter beams to make a triangle.
As you can see in the photos the point at which the two sides meet (height is interior about 19.5 feet) the man who designed it has no other structural members other than the triangular junction where the beams meet which is reinforced by quarter in solid steel gusset plates both sides of the beams and held fast with 24 very large carriage bolts. This creates a very strong, stable self reinforcing system that is tied together in the roof deck with more lumber than one would ever choose to use in these days of very expensive wood prices.
You cannot see the interior of the roof deck in the photos because of the finish of tongue in groove boards, but it has 2x4s laterally only 12 inches on center, then more 2x4s vertically also about 12" on center. Upon that the plywood sheathing is nailed. I would not even want to try to guesstimate the sheer volume of boards and hop my insurance company is not also trying to figure it out for replacement costs.
The high/long side of the roof passes through an exterior wall and rests upon that rotting header in the lanai, it spans 36 feet with two masonry columns 12'8" on center and I suspect they did not isolate the wood from direct contact with the concrete and in this hot humid climate resulted in the rot at the point of contact. In one spot the beam is actually entirely gone, on of the rafters is "floating." But all of the rafters are resting on a header that is very marginal to downright unsafe.
The roof does groan and pop and creak with thermal expansion, but has so far not even sagged a little. It is a testament to the level of overbuilding I think. It is built and cross built so over the top that it has held up in spite of that rot.
I know the rafters need to be jacked up slightly and supported so the old 3 piece exterior header beam (the joins are in the middle of the masonry columns mentioned above) can be removed and replaced, and the very tips of a couple of the rafters have been contaminated with the rot and will also need to be replaced, new ends spliced in. I am open to suggestions as to how to splice those esthetically.
What I am not sure of is where these long rafters pass through the exterior wall at about 17 feet up that wall there are four doors of pocket sliders which must have a MASSIVE header of its own over them. Out in the lanai the rafters come down to the header but there is also a pergola style pool enclosure with 4X10 beams out over the entire width of the pool, and it strikes me as far too much wood to merely hold up what amounts to window screens. Those also rest on a matching 4X12 by 40 foot long header that has 3 masonry columns 12.8 feet on center. As I say, that is a lot of wood for just holding up screens. So, I am thinking they must also play a part in the structure of the house. Because where the rafters meet the rotted header, and then also bolted to that are the beams out over the pool, there are beams running from the exterior wall out to the terminus of the rafters so that there are three 4X10 beams all bolted with carriage bolts to each other.
The stringer from the exterior wall rests upon the rotted beam, the other end rests on the header over the pocket sliders inside the exterior wall. It would have no function in engineering that I can fathom if it is not under tension. And also inside the wall has an upright member to make a second triangle for added support to the rafter. I cannot tell without striping away the drywall. But essentially the main roof rafter ends on the rotted beam and is bolted to this stringer and to the pergola beams, so that the three together would be securely immobilized from becoming mechanical. The stringer under tension and the pergola beam under compression. Like I say I can't imagine that they would have used such heavy beams over the pool just to hold up screens, they must have another function.
This is the crux of my problem, if those two beams which are bolted to the rafter do have a structural job to do then the plans by the company doing the repair will have to be revised. They intend to demolish the entire pool enclosure and replace with a more open mansard roof pool cage. One that is supported by an aluminum screen enclosure on one side and a super gutter on the other. They will delete the huge 4X12 and all the beams across the pool as well as the 3 masonry columns. Those also seem to serve no purpose other than to hold up the huge header on the other side of the pool.
Again, why would an architect/engineer design a pool enclosure with so many extraneous, not particularly structural columns and beams if they were not somehow part of the main house design?
So the photos will show how my house solved the roof design, but then opens up a lot more questions about overall engineering and architecture. Have a look and comment on what you see.
Structural engineering through an internet forum is asking for trouble. Your place is so far from standard build that the only way to check what is holding up your house is pay a structural engineer to check it. Having to demo a bit of drywall is much better than having your roof fail.
My guess is the ties/beam/columns in the 4th picture are what is holding up your roof which means they can't be removed. You can probably remove some of the columns if you replace the beam with a larger LVL or steel wide flange beam to clear span the space.
P.S. I'm in much colder climate here, but beams only ever fail from water damage. I've never heard of heat or humidity damage. You could have a roof leak or some major air leaks by the beam which is causing outside moist air to condense when it meets cold interior surface.
TY Akos. The columns that the repair design call for removal of are on the other side of the pool and not pictured. I will update this post with a photo as soon as it gets light enough out to take one. If they have any structural mission at all it would be to provide the pergola style enclosure beams to act under compression to immobilize the rafters.
The seller had hidden the defect and lied about it, he claimed that there was rot in the beams out over the pool but that they could be easily repaired and all they did was hold up the screens anyway. He claimed he had a man quote him $5 thousand but the guy took off for Ohio the minute they declared pandemic. And he was right about one thing, I called and texted and sent e-mails and NOBODY in the industry here was working. I only even got one reply from a contractor and he refused to give an estimate without structural plans.
I did get an engineer over at one point who was working, and I explained that what I wanted for the beam replacement was cypress. He laughed and said you can't use cypress, it is a decorative wood, not structural, it can't carry the load.
Well he was a new arrival from the North East, he was thinking knotty cypress where down here in the south yellow cypress is used for structural members because it is a local wood and is as strong or stronger than cedar, also has excellent rot resistance. It is an oily wood. But, it told me that he might not be the right engineer for the job.
Well, Covid seems to be about over and the governor reopened the state early last year so more people are working, but there is a building boom going on and there seems to be waiting times of a year or longer. Also the cost of materials has more than doubled, even tripled, it is going to have to be financed and that has turned out to be very tricky as well. The VA is blocking my access to the equity, they will not allow me to refi a house that is in need of a repair. I know that is not a structural topic, but it is playing a role here. As an academic discussion of the structural issues it plays no role, but in truth all projects have to be cost effective or they remain just theoretical. It is possible that this repair would cost me as much as $175 thousand, and that is just crazy. I would have to walk away.
As far as getting advice on the net, I will not be the one to make the decisions on what is torn down and what is replaced, but I do want to understand and have opinions perhaps of things I had not thought of. For example I would really rather not see the columns on the other side of the pool torn down. The beams over the pool yes, if possible I would have gone, they are too large, claustrophobic, and exposed to too much moisture, weather and pool evaporation and such. We are tropical at least 6 months of the year. It rains a lot starting in May and running often through Halloween.
There is a lot of knowledge here and I am hoping some others will see the issues and comment on them. I also was hoping the OP would check in occasionally and comment about what he finally has done with his plan, though it was 2018 so he is probably not checking here anymore.
Attached are 4 more photos. They show the proposed mansard roof pool cage that will replace the pergola style structure there now; the enclosure and lanai from another angle; the construction of the roof deck that is being supported, and the rot.
You can't see it really from the photos but there is weight bearing down at the exterior wall, because the pocket sliders will only partially open. That is why I think there is support for the rafters behind the drywall. If there were none the weight of the wall would not be enough to push down on the massive header over the door span. And, the width of the sliders is 16 feet so the header must be really huge.
If finances are tight, I would keep to fixing only what is necessary. In this case that is the structural work.
Looking at the rotted beam, that is a simple jack up, shore and replace. You should be able to find a contractor to do that as it is very common failure on porches. I would have the engineer spec a PT LVL or PT lumber beam and clad it in wood to match the house to avoid future issues.
The mansard pergola makes a very ugly valley against the house roof. In an area with a lot of rain, that is asking for trouble.
Akos, I laughed a little when you said the new mansard cage is very ugly; I would wager my equity (that the VA is not allowing me to tap) that you do not live in Florida. If you lived here you would have a cage, esthetic ideals or no, we have an opposite weather pattern from places like California. I had a pool there also and it was not caged, nobody I knew with a pool had a cage there. Too dry in summer for mosquitoes and too cold in winter.
Here though they are a must, we have disease bearing mosquitoes the size of hummingbirds. And that is just one of the pests that loves to hang around pools. I also frequently find scorpions IN the water, they can breathe through their armor for a time so can sting you underwater. If it were uncaged we would have snakes in the pool as well, and we have coral snakes here as well as water moccasins, and three kinds of rattlers. During the dry season other critters would come to drink and fall in.
Also, the deed restrictions require a pool enclosure. If the HOA did not require them insurance would.
But, as to the structural aspect, the house side of the new cage rests in what is called a super gutter. It is a 7 inch trough rated strong enough to be structural as far as a light aluminum cage goes, at 7 inches there is room for both the aluminum and the vast quantity of water coming off the roof in tropical downpours. I am sure that is why the original beam rotted in the first place, because of the pergola style enclosure it had no super gutter. The standard dripline gutter you would see anywhere in America was just woefully inadequate to the sheer torrent of rain coming off the roof and the gutters all around the house would overflow.
This is something to keep in mind when doing clerestory roof systems. My house is 3,545 sq. ft. under roof, something like 73 squares of roofing material. When it is raining at more than two inches per hour which is probably 100 days per year even a super gutter is taxed to get rid of it all. Normal gutters are just useless. Add to that the exceptional high humidity that does not allow for wood to dry out between soakings and rot is a certainty unless you have painted redwood. (I checked on the price for redwood from a mill in Sonoma County where I used to live, last year it was $55 per foot a for 4X12).
As to the rest of your comment it is spot on I think and I was very tempted to go the replacement of like for like without benefit of county permits, after all they are the ones that destroyed the blueprints, so they really cannot say that anything has been changed.
Finding help though as you suggest is just out of the question, the unemployment rate in the house trades here is zero. They are grinding out house after house at a rate unseen before. The housing vacancy rate in the greater Tampa region is less than ONE WEEK! Houses put on the market now sell in 5 days or less for over asking price. Especially pool homes. Very often they sell the same day they are listed with RE agents having a list of buyers waiting for something to come on the market. I would have thought that would have cooled with the higher rates but if anything the higher interest on mortgages seems to be driving panic buying before they get any higher.
The simple jack up, shore up, and replace is what I had wanted to do, but the tips of at least two of the rafters are also compromised from sitting on rot. How to replace those is something that even a pro would have questions about. I have done some framing in my youth but never real carpentry and it was one of the things I was hoping to get opinions about.
The tips of two or possibly three rafters will have to be cut away because if they are partially rotten then there is no point resting them on a fresh new beam. And that will not be simple because the roof deck is nailed securely to them. A sawzall can take care of the nails but then how do you reattach the roof deck to the new rafter pieces that are fitted in, and how are those new pieces spliced in so that they meet or exceed the original solid rafter?
My idea on that was just a simple "L" shaped * (1/2 inch should be adequate? Opinions?) bit of steel that could be bolted to the old rafter bit and the new. I do not know if there is a term for that in carpentry but I think of it as a reinforcing bridge, or like a cast for a broken leg.
The contractor that does pool cages and is also a licensed contractor for building and repair says that this is going to be the tricky part, also because the roof is about one and a half feet beyond the end of the rafters and previously were held up by the beams over the pool, though the weight is negligible, but there will have to be some kind of cantilevered extension to carry that weight, it will not do to just leave about 18 inches of eves hanging out over thin air. Even though like I said the weight is negligible.
Yes, finances are tight, I am a 100% disabled vet and I would have been decent labor last year, but then had a major bypass operation last year that left me barely able to walk, so I am having to hire.
It also means a fixed income in a time of very high inflation. Homeowner insurance was about 1,500 last year, 1,868 this year, and $3,445 next year. Between the premium increase and the resulting shortfall in the escrow account I expect my house payments to rise by well over $300 per month starting in April.
And that is just the insurance. As bad luck would have it my insurance company is exiting the market so I had to get a new 4 point inspection for the new insurance quote, and they are ruthless if not downright crooked here with those. The roof is only 11 years old, it was installed using 30 year rated asphalt shingles, and the 4 point inspection claims that there is degranulation in a couple small spots, the inspector showed them to me and I say they are about 5% of the roof, with 95% looking near new. The degranulation is consistent with a roof that is 11 years old, it is not excessive. But, having noted that the new insurance company I am told will only issue a policy for one year as a non renewable policy till the roof is replaced. At more than 72 squares I cannot afford both the insurance, new roof, and rot repairs at one time. Especially with the VA blocking access to the equity.
I am on a knife's edge of being forced to sell rather than save my house. If I have to sell I would not likely get a lot of that equity since I would have to make allowances for both the roof and the repair, I should not have to tell anyone in America what happens to disabled vets forced out of their homes. There are enough homeless vets in the US for people to understand it does not end well for the veteran. Seriously, with the VA blocking access to the equity which makes zero sense since then they would be required to pay off my mortgage and take the house as REO, you would think they WANT vets to go homeless.
A $25,000 FHA Title I Home Repair second mortgage over 20 years was approved until the last step in that process, which was to send the lender a copy of the contract for repair. They saw the words "DEMOLISH POOL ENCLOSURE" and cancelled the loan because they do not lend for "luxury items." I did try to explain the pergola structure rested on the rotten header and had to go in order to get at the beam but they were not remotely interested, as long as the word pool was in the contract they were having nothing to do with me. When they approved me was when I signed the contract to have the work done, but even though I had paid the upfront costs no work was ever done, because the loan was cancelled.
I also was approved for a cash out refi last November at 2.125% interest which is even lower than the current mortgage at 2.25% but that was when the VA said they do not give home loan guarantees on houses that need repairs. So that loan was also scuttled. Then I asked my credit union for a HELOC but because as a 100% disabled vet my income is tax exempt they said it does not meet their debt to income guidelines. My net income is adequate, but my gross is the same as my net and thus they say it is inadequate, the gross is all they care about. If I were a taxpayer I would have qualified. Mind you the equity, the market value today less outstanding mortgage is about $155 thousand in equity, but again they just are not interested in that.
I also had to trade my older car in for a new truck last October, it was becoming a maintenance headache, and the darned dealership submitted the loan application to 15 different banks torpedoing my credit score by 42 points overnight. That should be illegal really but there is just nothing the consumer can do about it. That is one thing about Florida, it has benefits, I pay no property tax here, but also has deep red state lax laws regarding consumer rights. And insurance regulation. That is not really pertinent, but you see what I am dealing with and I have to say, I am feeling like a milk cow about now. :)