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CarolVentura
Registered Users
Posts:18
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| 12/07/2007 7:47 PM |
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| Our ICF roof is almost finished, so I'm looking for solar options. It looks like SolarSeal LINK would be perfect for our southern facing sloped concrete roof LINK I was wondering if anyone knows if it is a good product or if there are better options. |
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Quantum
Registered Users
Posts:262
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| 12/08/2007 9:27 AM |
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IIII don't know about that stuff. He sells an elastomeric coating in which he says you can embed solar panels.
First of all, roofing is not a place where you want to be messing around with some guy's majick potion. Second, you're gluing in your modules; what if you need to move? No way to take your expensive system with. Third, there's no way to tilt the panels for optimum; check this, to see what that means. Fourth, all these thin-film panels are relatively inefficient so you need alot of roof area; and the economics are questionable. Fifth, you'd better make sure no one walks on the panels.
If it were me, I'd use waterproof concrete and buy the most efficient panels available (Sanyo 16.2W/sqft, SunPower 16.42W/sqft), and add on as I could afford it. Tilt for optimum. CIGSSe will soon hopefully overtake silicon panels in efficiency, freeing us from this limited resource and likely be cheeper. |
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CarolVentura
Registered Users
Posts:18
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| 12/08/2007 9:40 AM |
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I need to put some sort of roof over the concrete slab anyway. I was going to use a metal roof and attach regular solar panels to it, but unfortunately, the slab was poured with 2% calcium chloride in it and is already effervescing. Not only will the salt eventually attack the stainless screws, it will also corrode the metal.
I will never need to move the panels. If I sell the house, the solar components will be left in place. The slope of the roof is already the correct angle and no one will be walking on it. I’m not sure about the efficiency, though, or if the product is as good as it sounds. That’s why I asked the question. Thanks. |
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Quantum
Registered Users
Posts:262
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| 12/08/2007 12:36 PM |
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Another issue I forgot is the heat load that direct-mounted solar panels add. Rather than a white reflective surface, they are black and add considerable heat-load to the substrate. Any coating will need to tolerate this, and be aware that the concrete will heat up as well since there's no air gap. Studies indicate that mounting reflective surfaces on roofs can save as much as 20% in comparison with darker roofing materials.
Efficiency is going to depend on the panel you choose. He suggests several products, but most are thin-film so will have much lower efficiency than the best, just so you know. Assuming you have enough roof area to meet your generating goal, you should compare the cost with a similar capacity of high-efficiency panels.
Calcium chloride, although a salt, is unlikely to corrode stainless screws for the lifetime of the panels, maybe for the lifetime of the structure, particularly in those concentrations. |
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CarolVentura
Registered Users
Posts:18
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| 12/08/2007 1:15 PM |
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| I have plenty of roof area since there is no ridge, just a VERY large, south-facing sloped concrete roof. Having lived 5 miles from the ocean in my youth, I know how salt in the air corrodes. We couldn't use our fireplace after the heatilator rusted shut! I assumed that a metal roof wouldn't have a chance, being in such close proximity to the salty roof. I know that a liner would be placed between the concrete and the metal, but I have seen what salt can do to metal all too well. I'm open for other suggestions. Thanks! |
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Quantum
Registered Users
Posts:262
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| 12/08/2007 1:42 PM |
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Not sure how close you are to the sea now, but if at least 5 miles you can use about any roofing, including standing-seam. Just some cheap asphaltic felt first, or tyvek to isolate concrete from metal would be fine. This isn't New Science; it's done all the time. Good news about a metal roof is you can also add rainwater catchment for toilet flush and landscape irrigation, as the runoff is quite clean.
But there's always modified bitumen, and there are some new plastic membranes being used as well. I'd avoid PVC panels for this, as I've got to think they'll oxydize and/or crack over time.
Whatever it is, it should be as white as possible to reduce heat load. |
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CarolVentura
Registered Users
Posts:18
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| 12/08/2007 2:04 PM |
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| We are far from the ocean now, but I thought the salt layer that is forming on the concrete slab would eventually penetrate whatever is put over it and corrode the metal roof. I was originally planning to use the raised seam metal roofing that allows solar panels to be attached to the seams, but the salt is scaring me away from that option. |
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PatrickT
Registered Users
Posts:138
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| 12/19/2007 4:17 PM |
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Carol,
Did you use anything to stop thermal bridging where concrete roof meets the ICF walls? We are also building an ICF but with a flat concrete roof. I'm looking for a material that will isolate the "cold deck" roof.
Patrick T |
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Quantum
Registered Users
Posts:262
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| 12/19/2007 4:55 PM |
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Patrick, Amdeck is ideal for this, as it is designed to be used with ICF walls.
LINK
By the way, to the Mod of this forum, I believe that the reason you change all embedded links to LINK, is so people can see them better. Why not set underlining of links in the forum software instead? Wouldn't this save you alot of trouble rewriting the links? |
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CarolVentura
Registered Users
Posts:18
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| 12/19/2007 7:03 PM |
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ICF panels support the concrete roof, so the bottom is insulated. I'm still not sure what I will put over the slab to insulate it and still be able to add solar panels. If you could put a rubber roof over a layer of foam panels glued to the concrete, then you might not need to deal with thermal bridging. I suggest a sloped roof rather than a flat roof, though, because flat roofs often leak. |
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Quantum
Registered Users
Posts:262
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| 12/19/2007 8:13 PM |
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Carol, I don't remember your configuration, but you could have EPS blocks cut to a slope, to give a slope to your roof, as well as insulate and isolate that eflorescence if you're concerned about. Over that, a steel roof, or cement-fiber shingle roof. But I wouldn't use the rubbery coating. It won't last like drawn butyl or modified bitumen; and when you need to replace the roof, it will be impossible to unstick.
Just trying to help. |
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CarolVentura
Registered Users
Posts:18
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| 12/20/2007 9:20 AM |
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| The ICF blocks were cut to a slope. You can see that at LINK. I want to put solar on the roof and that is the problem. I found out that a metal roof would have to be raised from the concrete on strips because it would interact with it. The solar guy said that the panels couldn't be attached to the raised seams as usual because the strips and metal roofing would not be secure enough on concrete. I can't put panels on a rubber roof because the penetrations would void the roofing guarantee. I'm looking into the possibility of gluing flexible solar components to a rubber roof. What I don't like about gluing flexible panels onto a waterproof coating is that there would be no insulation on top of the slab and - as you have pointed out - the roof would be difficult to replace. Plus, the coating has to be reapplied around the edges and to the rest of the roof every few years. There is not enough slope for a tile roof - plus - putting panels on tile is a challenge, too. I'm still looking for an answer and would appreciate your suggestions. |
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Quantum
Registered Users
Posts:262
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| 12/20/2007 11:02 AM |
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Wow, very nice photo essay Carol.
OK, so you have a slope, good. So flat EPS panels will do; much cheaper. One thing to remember is that when the deck concrete no longer gets wet, it will no longer effloresce.
I am not a roofing engineer, so take this for what it's worth. I would do this:
- Wash that roof with diluted muriatic acid, rinse, and let it dry for at least a week.
- Then glue down EPS panels with a standard roofing mastic to the concrete, 100% coverage. Make sure it's a non-solvent-based mastic, usually a water-based "emultion", or else it will melt the foam. Use at least 3" foam ( ~R4.4 for each inch, plus the concrete's thermal inertia will give good thermal isolation), with at least 1.5x density, maybe 2x. Foam all seams in case there's a leak in future.
- Put down two layers of standard roof liner or one of DuPont's RoofLiner, with barbs or large staples into the foam.
- Put on a standing-seam roof using long Tapcons screwed into the concrete.
- Use thin-film solar sheets in the roof, or install a frame with large surface-area footers, fastened to concrete with Tapcons.
This should give you a triple water barrier, decent wind resistance, and insulation. There are probably better ways, and I hope people will speak up, but this is my suggestion.
Out of curiosity, exactly how many days did they leave the OSB in your Speedfloor before removing it? Concrete still looks green (dangerous), although if they leave the wood on too long it will stick. |
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CarolVentura
Registered Users
Posts:18
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| 12/23/2007 11:53 AM |
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Thanks for the advice. To answer your question about the Speedfloor:
The floor cracked on the sections where the OSB was removed a week after the pour and also in the parts where the OSB was removed months later. I'm not happy with the results because the floor vibrates if you jump on it over the rooms with long spans. Those rooms will be used as art studios, so the floor needs to be strong. Consequently, I'm going to put posts under the middle of the long spans (in the garage and kitchen). It might not be necessary, but I was taught to plan for the worse and hope for the best. I'm much happier with the ICF roof. It's more expensive, but very solid and quicker to install and will be easier to finish inside with sheetrock. I chose Speedfloor between the first and second stories because I need space between the beams for the HVAC and utilities. |
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Quantum
Registered Users
Posts:262
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| 12/23/2007 12:30 PM |
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I see. I'm sorry to hear about the cracks; I've never trusted Speedfloor. So it even cracked after a month with form? Is it 4" thick? Were the cracks down the center between joists? Had they cut relief joints in the concrete? If so this might be a concrete quality issue. Maybe low-shrinkage concrete would have prevented it.
It is wise to put one or more columns below. The good news is a bit of 'give' is always good for a floor. Much healthier than solid rock.
I've heard that ICF roof is alot more expensive, like $16/sqft, but you imply not so much? Is that LiteDeck? Were the tophats from LightDeck? I certainly do not like the rails supported only by EPS, without rebar as you had done. Design flaw. |
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CarolVentura
Registered Users
Posts:18
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| 12/23/2007 1:02 PM |
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| They did not cut expansion joints, even though they promised to do it the next day. There are MANY cracks - some going diagonally from holes I put in the floor for vents (as expected with no expansion joints) but most cracks run along the top edge of the beams. Only 6" mesh is called for - and that is embedded in the bottom of the slab. I asked for rebar to run perpendicularly over the beams, but my concrete guy said that there wouldn't be enough concrete to do that since the Speedfloor is embedded into the slab. I'm sorry I didn't insist, because with the 3 1/2" to 4" pour, there was enough room. He did add some rebar between each beam, as I requested. I should have asked for more, though! The ICF roof panels were VERY expensive - even more than the Speedfloor. Add yes, the tophats are also LiteDeck. |
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Quantum
Registered Users
Posts:262
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| 12/23/2007 1:16 PM |
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Sounds like a combination of shrinkage and lack of those cross-members you'd wanted. Even with proper measures though, the floor would bounce, assuming the standard 48" spacing. Half that would greatly reduce bounce & cracking, but would greatly increase cost. Ah well. Were live- and dead-load calcs done by SF? Did SF give recommended install method in detail?
So even where they'd left form on for 30 days, cracked? Differently? |
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CarolVentura
Registered Users
Posts:18
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| 12/23/2007 1:36 PM |
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| You can see the installation at http://iweb.tntech.edu/cventura/Floor.htm The temporary metal pieces that go between the joists and support the OSB are designed for a 49.5" space, so it would not be practical to have less space between the joists - even though I could have done it since the rooms were not exact multiples of 49.5". In fact, I could have reduced the space by several inches in most of the rooms. The OSB was difficult to remove in one of the smaller rooms (a bathroom) because of the many foam pieces embedded for the plumbing that stuck to it, so it was in place for a few months. That floor actually cracked more than the other floors! Speedfloor provided the installation method and rented the metal supports. They were not very helpful, though. In fact, their web page showed the product with a different hole configuration and they could not answer many of my questions. They also reversed the direction of the beams in one room and I didn't notice it in time - which will cause me headaches when installing the plumbing. They never suggested placing them closer or that the floor would bounce. They said that the product was used for parking garages and made is sound great! |
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Quantum
Registered Users
Posts:262
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| 12/23/2007 2:11 PM |
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It'll be fine, especially since you understand the issues. Next time. (?) Email me if you'd like to know some better flooring systems.
I'm betting the floor where OSB was left for 30 days shows only shrinkage cracks. Should have been scored, or low-shrink concrete used. But this will be just fine. It's not like it has to be water-tight.
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PatrickT
Registered Users
Posts:138
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| 12/24/2007 9:31 AM |
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Quantom,
My question concerns a "cold" roof deck. In my project, I will have a roof top patio. I'm using an ICF wall system with 4-5/8" foam on the outside/8" concrete/2-5/8" foam on the inside. The roof deck is a Hambro steel bar joist resting on the 8" concrete wall. The roof slab will be on top of the wall. Then a 3.5' parapet wall will be poured. My plan is to insulate from below, 16" of space from bottom of slab to sheetrock ceiling. I prefer not to have my insulation on top. I feel the foot trafic and the roofing methods will get much more complicated. Also, I can use so much more insulation from below. The issue arrises from the fact the cold roof is thermally conected to the ICF wall. With the majority of the insulation on the outside of the ICF, my concrete will be best looked at as inside the heated space.
Ideas I've had to "isolate" the 3 thermal paths where walls meet roof deck; 1) Steel joist (apprx 4' OC), 2) Roof slab between joists, and 3) Rebar bent to connect wall/roof. from a loading point of view, the slab to wall is low and could be isolated with a thin layer of dence extruded foam. The rebar could be fiberglass Rebar. And the joists could rest on 1/4" fiberglass sheet cut to the size of the joist foot.
I also face this problem where an outside suspended concrete deck meets an ICF house. By using radant heat on the main floor, I must prevent the heat from escaping into to the walls and outside deck slab. But in this case, the walls are less of an issue because as I have stated above, the ICF wall concrete is inside the thermal envelope. The slabs in principle can be isolated by a foam expansion joint directly over the center of the wall. But if the slab/s are thermally attacted to the wall, it just goes down/up to the ICF wall. It maybe hard to imagine this scenario, but if you sketch it out it becomes clear.
I have called both Hambro and lite-deck. Neither had ever heard of the issue.
Patrick T |
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