Membrane for Waterproof Porch


#1

I’m planning a two-story garage. I’d like to have a second floor exterior porch that is waterproof to protect the garage door opening/driveway area below. I’m waterproofing mainly so I can use the driveway area as an extension to my shop even in bad weather. I’d like to be able to run power and light fixtures underneath the porch.

I’m planning on framing the porch area with 2x8’s on 24" centers with 3/4" T&G exterior grade plywood. I’m going to slope the deck at 1/4" per foot away from the garage. The porch area is 8’x18’.

I’ve seen an article in FineHomebuilding about an EPDM membrane in a similar situation. They installed it over a fiberboard base that was fastened to the plywood subfloor with screws and large specially shaped washers. They protected the membrane with duckboards and a removable frame (that was ripped to level out the slope.) It was a pretty slick install, I thought.

My question: do I need this fiberboard stuff in this case? Is there another product (peel&stick? liquid EPDM?) that I could apply directly to the plywood and then cover with a duckboard frame? Has anyone seen a duckboard install of this size?

I’ve seen some mention in this forum about rubber tiles for placement over membrane roofing, does anyone know a brand name for these things?

Thanks for any comments.

Dave


#2

hello dmilamj,
the roof you use should depend on the use of the roof.
if you are going to be walkin around alot on the roof over plywood,
then you will need somethin more durable then plastic.
if its just going to be a roof then peal n stick or epdm will work.
but again if you goin to be trompin around on it up there
then get a torchdown or ,three ply glass coated roof( hot tar).

good luck.

gweedo.


#3

Gweedo,

So have you ever seen EPDM or peel&stick used as the waterproof membrane and then covered with something more durable as the walking surface, i.e. rubber tiles or duckboards?

Dave


#4

A polyurea sprayable membrane with a broadcast aggregate for slip resistance works well, but is not DIY.


#5

peal n stick stuff hasnt been out long enough to really know.
i just dont think its thick/strong enough to handle it.
as far as epdm. it has been out long enough and i have torn off many
that have failed in this application.
plastic and rubber may last a lond time in the cold. but the heat destroys it no time down here.

gweedo.


#6

As I’ve mentioned in an other post dmilamj, in the UK we use what we call a promanard tile. It is designed for placing over any kind of roofing membrane on flat roofs, thus protecting the membrane and allowing foot traffic. The tile is 12"x12" and is interlocking. If the tile or something similar is available in the US, then maybe someone like gtp1003 or Dennis will be able to give you some pointers, good luck.


#7

The person you would like to listen to would be Dennis, Aaron B, or Gtape. They know the flat roofs 10 time more than i do.


#8

Aaron can he torch it or do hot and then put some walk pads on it?? i see it a lot over here where this commercial buildings need constant foot traffic for ac units maintenance… usually is a multi-ply built up roof … Peel and stick will probably leak if pads block the flow of water … I am not a flat expert… Aaron seems to know his flats pretty good :wink:


#9

I had no idea this would be so complicated. May be more trouble than it’s worth.

How about something like the Dex-O-Tex Weatherwear product? Looks like a complicated installation, probably not DIY, but designed for this sort of application. Anyone have any experience with this product?

BTW, thanks for all the comments.


#10

Do you know anyone who installs this sort of system in the Houston area? Any brand names I could research?

Thanks a bunch.

Dave


#11

I’m assuming you are wanting to contract out the work? If so, you have a few options. Like mentioned above, you could go with a modified bitumen, but if you do I would recommend a cold-applied system to avoid the possibility of burning you garage down. The APP modified bitumens (typically torch-down) are better than the SBS modified bitumens (typically mopped down in asphalt). Then there are the modified bitumens you can cold-apply and even some peel and stick membranes. If you go with the modified bitumens, then I would recommend a cold-applied APP modified bitumen with heat-fused laps. The contractor can heat-fuse the laps with either a torch or a hot-air gun.

Now, lets look at your other options. Yes, you could go with EPDM, but that is a very unforgiving roof system. If I were installing it on my house I would want to be the one doing the work, because it is too easy to screw up from a workmanship point of view. The good news is that with an 8’ x 18’ roof area, the EPDM can be installed with a full sheet and no seams. However, there is the question of flashing the perimeter of the roof. Will you have a wall on one side and three edges, or what? As for the fiberboard, that is needed to protect the EPDM from nails backing out of the roof deck, and will help the roof system absorb some punishment. In addition to the fiberboard, I would probably install recycled rubber walkpads prior to your duckboards. In commercial applications an extruded polystyrene insulation is typically used, but walkpads could work for you.

Other options I would recommend include PVC (Sarnafil only), or even a TPO. You could conceivably use a peel & stick ice & water shield, but you would have to cover the membrane from exposure to UV solar radiation (sunlight). If the duckboards are easily removable, you could almost do this yourself but lapping the membrane is critical. I would stay away from any liquid or spray applied systems since the substrate (plywood) is not suitable for those roofs.

As for contractors in the Houston area, there are several depending on which way you want to go.


#12

[quote=“dmilamj”]

Do you know anyone who installs this sort of system in the Houston area? Any brand names I could research?

Thanks a bunch.[/quote]

Many Spray Polyurethane foam contractors do this sort of membrane since it requires the same plural component heated proportioning equipment to do it.

Look for SPF roofing contractors, uretname coatings contractors, and polyurea coatings/membranes contractors.

Once you find one, send me a line if you need more info.


#13

Look into hydro-stop


#14

Hydro-Stop is not a bad product from what I’ve seen of it, but it is more of a coating and probably wouldn’t work best in his situation unless he already had an existing roof membrane to coat. I suppose he could install a smooth-surfaced mod. bit. and then coat it, but cost-wise it wouldn’t make much sense. Once again, I would stay away from the coatings and SPF applied directly overtop plywood substrate.


#15

[quote=“Cerberus”]

Hydro-Stop is not a bad product from what I’ve seen of it, but it is more of a coating and probably wouldn’t work best in his situation unless he already had an existing roof membrane to coat. I suppose he could install a smooth-surfaced mod. bit. and then coat it, but cost-wise it wouldn’t make much sense. Once again, I would stay away from the coatings and SPF applied directly overtop plywood substrate.[/quote]

Is Hydro stop an elastomeric acrylic?

I agree that cost wise the mod bit and a coating could be cost prohibitive.

Did someone suggest SPF over plywood?


#16

Cerberus and AaronB, thanks for your comments; y’all give out excellent advice here.

At first I was considering doing the install myself, because as you mention, I would be very careful with the edge flashing and others install details. I could afford to take my time, and some of the membrane installs don’t look too complicated, just detail oriented.

I’m starting to wonder now, though. Even if I figured out which system I might want I don’t know who might sell me the membrane and adhesives.

“Will you have a wall on one side and three edges, or what?”

That’s right, one 18’ side is up against the gable end of the garage, the other three sides are edges. So careful flashing along the garage side, and then edge details and probably a gutter along the long edge.

I just talked to a guy from N.A.H. Inc. about Dex-O-Tex Elasto-Tex 500. He rough quoted between $2-3k for the deck job, withut flashing (I would do the flashing…) Anyone familiar with this product? How about the price for 144 sf, that’s between $14 and 20 a sf.

So here’s the system I’m thinking about installing myself:
3/4" plywood deck
fiberboard (1/2"?)
EPDM membrane
recycled rubber walkpads
duckboards (probably ripped treated 2x4 sleepers, trex or cedar deckboards screwed to sleepers from the bottom of the sleepers with brass screws, the duckboards will be held down only by edge trim around the railing and walls, no penetrations of the membrane.)


#17

Where in Houston do you live? I’m on the west side over near West Oaks Mall.

Anyway, EPDM with a protection course of recycled rubber walkpads should work fine for you if you are familiar with how to install EPDM. If you have any more questions about it, let me know. EPDM was one of the roof systems I used to install back when I was actually doing roofing instead of consulting. Of course, BUR and Mod. Bit. roofs are better, but for a garage roof the EPDM should be fine. Make sure it is .060 mil thick EPDM, and that it is black and not the white EPDM. The black EPDM has more carbon-black in it and holds up much better to UV.


#18

Cerberus, I’m up in the Heights, about a mile north of downtown.

I may be making this too complicated. I need to remember that this is a porch over an unoccupied space!

What if I went with a Self-Adhering product like Johns Manville DynaGrip Cap or Polyglass Elastoflex SA P G? Then I could cover that with a wear layer of either thin concrete pavers or duckboards with rubber padding underneath. Looks a heck of a lot cheaper and easier for me.

Thanks for all the help, guys.

Dave


#19

I’m obviously not familiar with you background with regard to construction/handyman/roofing. However, the truth be known, if I was you I’d just get me a roll of Grace Ice & Water Shield and adhere it to your wood deck. As a consultant, I would not suggest such a thing to a client since I have to cover my ass. All the same, Ice & Water Shield can be used like the old GRM roofing material. GRM didn’t do so well, but since it is over open space and is easy to repair, it may be the way for you to go. If you ever develop a leak, you would just need to clean off the membrane and peel and stick a new piece of material over the hole/leak. You will need a roller to appy pressure and assure you seal the seams, but it is a pretty simple system. The main thing is you can NOT leave the material exposed to UV. Cover it with walkpads, extrude polystyrene, or even Meadows board, and install you duckboards. I would not use pavers without knowing your deadload capabilities of the structure.

When do you plan on starting the job? I have friends in the Heights, so if you catch me on a good day I might be pursuaded to meet with you once you are ready to start. Don’t hold your breath, as I am usually really busy, but if you catch me at the right time and I’m in the area you might get lucky. Needless to say, it is better for me to give you advice if I actually see the project.


#20

its a house porch.
torch it down with a wood deck over it.
done deal.
gweedo.