Air-Sealing, Waterproofing, and Insulating Between Unconditioned and Conditioned Rooms
I have a screened porch (deck) above a living space (bedroom). I know there are lots of articles about ceiling strapping, as well as why one should not have decks above living space, but I could not find a discussion applicable to my situation.
Climate Zone 6
Covered Screened Porch ‘above’ bedroom
Standard construction wood framed house, interior insulation
I’ve read many articles indicating it is a bad idea to put living space below a deck or screened porch, but this is the design, and our builder has worked with a subcontractor who has built custom showers for decades, and has done these porches before, and guarantees it won’t leak. Imagine a square room with one quarter exposed on two sides.
1) Ceiling strapping:
After it was too late, and even though we discussed in person, I learned that my understanding of ceiling strapping was different than my builder’s, such that he built an entire basement ceiling frame underneath and parallel to the existing upstairs floor joists. In my experience, I’ve only seen 1 x 3 screwed to existing joists, whereas he created an entire new structure … I’m sure there are good reasons … air separation between floor and ceiling, sound issues, footfall, room for more insulation, etc. but the amount of new 1 x 6s and then 1 x 3 attached to them is staggering and was shocking to see, and now I know why the cost of basement framing was exorbitant. We also lost another six inches of height. Luckily, we still have 8ft.
2) Screened Porch above – how to insulate
Since we designed a screened porch above this bedroom, the underside (bedroom ceiling) will need to be well-insulated, but there is now a massive amount of framing in the way. I would think we’ll have to spray foam it, given so many cavities, and criss crossing pieces of framing, or are there combinations of insulation material better suited? What about a vapor barrier, or is spray foam enough?
3)Waterproofing floor of screen porch (bedroom below)
If anyone has ideas about creating waterproof floor system, would be helpful, but I have found some helpful articles. The porch has two exposures, is in the woods, and we think there will not be a lot of wind driven rain. Screening will be 4ft above the floor, and open year-round. The new floor will be large tile, and have ever so slight a pitch, and the idea is to make a curb, similar to a walk in shower, between the porch floor and the living room floor, and flash the two inner walls, and have some sort of way to push water off the side of the house if necessary. I do know stepping over a curb is an ergonomically worse choice than a step up or down, but we may be able to place a floating ramp structure on the exterior floor, although I know ramps may be more of a tripping hazard than steps.
The other floor design idea was to install tapered roof insulation boards, then EPDM, then tapered sleepers, then roof deck, but due to the cost of labor, material, and the inability to sweep/remove debris that may fall between the deck board cracks, that idea is not going to be used.
A lot of info, welcome any and all thougts.
Thanks
articles:
https://www.jlconline.com/deck-builder/designing-screened-porches_o
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Replies
Stuartd,
It's the combination of three things - an unvented flat roof, screened porch and roof-top deck - that make this one of the most difficult and frankly risky assemblies I can imagine. You are creating a water-proof deck which will be penetrated by load-bearing walls, and at the same time exposed to the elements both inside and out.
I know this is the last thing you want to hear at this point, but there is no way I'd go ahead based on some guy saying he knows how to do it. I'm sorry, but beyond including the deepest overhangs you can, I don't have a lot of useful advice on how to proceed.
Hello Malcolm,
Thank you for your advice, which I certainly understand. Overhangs are 1ft, an amount which most of you would probably consider not even a minimum standard. To be clear, the space is fully covered by the pitched roof covering all of the house, with conditioned attic. The only load bearing walls are really columns which will support the roof at both perimeter sides.
stuartd,
Supporting it on posts simplifies things somewhat. When I've done these, one thing I try to include was good accessibility to the vulnerable parts for possible future repairs.
So a waterproof deck membrane extending up the base of the columns and house wall, and a finished surface of pavers, or decking in small sections, on spacers to allow drainage. Any screened elements should sit on top of this finished floor and be easily removable.
One of the other problems with these screened porches, which we see frequently here in GBA, is that over time the function of these rooms frequently changes. First to a three-season room, then often the desire to incorporate it into the conditioned area of the house. The demands of those spaces are very different - and difficult to reconcile with the work necessary to make the covered porch function. Just a heads-up for the future.
I agree with Malcolm; I've done similar projects many times and they are among the most challenging and risky things we deal with in residential construction.
This article by Emanual Silva is how I've usually done it: https://www.finehomebuilding.com/project-guides/decks/decking-over-a-roof.
The only safe way to insulate this assembly is with closed-cell spray foam. If you want to reduce your environmental impact, you can use a flash-and-fill system.
Curbed assemblies need to lead to either floor drains or scuppers. Both are challenging to get right, but it's possible.
The scope and complexity of this situation begs for you to hire a competent designer or design/build contractor.
Thanks Michael, the sub who is slated to do the floor/waterproofing 'has' done this design before, but I know, it seems risky. This upstairs floor is modular, and was craned in. We as owners simply did not want any number of off the shelf systems for a three season room, but instead want it exposed year round. Do you think plan B could be lining the perimeter with sliding doors (and appropriate railings)?
Michael,
I've done a couple. It's a bit easier here not having to worry about freeze/thaw - and we have milder demands on the flat roof assembly in our temperate climate but it's something I've now put down on my list of things I just won't design into a project.
Two months later, changed plans, used Duradek walkable roof membrane installed by roofer who has done this for decades. 'Curb' is about 3" high, and all agreed risk of water into living room is 0%, given it is a box with two sides missing, in the woods, not close to large body of water, so no slope needed, no complexity of building a deck on top of a deck.
Looking for ceiling insulation ideas here:
https://www.greenbuildingadvisor.com/question/screened-porch-ceiling-insulation-challenge
Thanks again for advice
No slope at all? Weird. I hope it works for you. Thanks for the update.
Yes, I am confident given the minimal weather exposure, it will be fine. (famous last words...)
Wasn't able to spray from underneath, did Rockwool, but the Duradek on porch floor is water and vapor barrier. Do you think that is sufficient and bedroom below will be fine?
Thanks
Stuart, I don't mean to sound flip. We all have different tolerances for risk. As a design professional, I need to recommend assemblies that are at minimum code-compliant and I usually try to go a bit beyond code in case something eventually goes wrong. I looked through the Duradek drawings (https://duradek.com/Downloads/Drawings/Duradek-Detail-Drawing-Collection.pdf) and they all appear to show a 2% slope. I did not read their literature to find out exactly what they require or what the consequences are if you deviate from their requirements. Like I said, I hope it works for you.
In climate zone 6 I would absolutely not specify or recommend a low-slope roof with only mineral wool insulation. I do everything I can to avoid foam insulation but this is one location where I do not compromise. There is a chance that you will find nothing bad happens, and in any case it will probably appear fine for the first year or first few years. It would be interesting to open up your ceiling in ten years to check on the conditions there. I would put money on moisture accumulation, mold and rot, but again I hope that luck is on your side and it works out for you. Hopefully you're at least using a high-quality variable permeance membrane on the interior to limit how much moisture can get into the assembly?
Thanks Michael, I understand and appreciate your advice, make sense. I also saw the minimum 2% recommended slope from Duradek, but our area rep/installer with decades of experience said in my project there was no need, given the environmental protection, trees, etc., previously described. He certainly would have required a slope for an exposed to the open sky, or other 'normal' rooftop deck factors.
It is not too late to remove the Rockwool, as no drywall has been installed. Is #1 recommendation a few inches of spray foam, then re-install the rockwool? Since this porch could be the main problem area in the house, I am willing to spend more to prevent issues.
If #2 recommendation is to use a membrane, are you suggesting the membrane be adhered directly to the ceiling of bedroom below (the underside of the subfloor of the porch)? If so, I would rather count on the experience of the spray foam installer vs. teaching my contractor a new skill required to install Intello or other such membrane.
Thanks again
stuartd,
I'd go a bit further than Michael and say you are pretty much guaranteed to have problems with the ceiling insulated the way you have within the first couple of years. You need a layer of impermeable insulation thick enough to keep the sheathing below the dew point.
This article explains why: https://www.greenbuildingadvisor.com/article/insulating-low-slope-residential-roofs
Malcolm, thank you as well, and for the article. I just replied to Michael.
"I’ve read many articles indicating it is a bad idea to put living space below a deck"
Great questions in the original post and lots of good information in the replies. I very much appreciate the knowledge and the links. I also acknowledge that the risk associated with this condition is indeed greater than having a properly installed, sloped roof over living space.
However...
Virtually every building in North America that has a flat roof (that would be most of our commercial buildings) is effectively a deck over living space. The only difference being that some of those roofs aren't given surfaces intended to take the wear of foot traffic.
I just wanted to point that out.
I think one of the reasons we have more problems with this in residential settings is that our builders focus on either residential or commercial and rarely cross over, or seem to learn from each other.
Thanks again. I just wanted to share the thought while I enjoy my morning coffee and read.