We’re SJRoofingVenting in leading roofing contractors in San Jose, and we’re going to show you how we do a gravel roof with a TPO over it — how that works and how good it is.
Begin with Insulation
Begin by laying the approved insulation with no gaps greater than 1/4 in. Versico recovery board and polyisocyanurate insulation with a thickness of 1 and 1/2 in or greater should be utilized.
Use a minimum of five fasteners and plates per 4 x 8 ft board. When using 4 x 4 ft boards, regardless of the thickness, a fastener and plate are required every 4 sq ft. Please refer to the details for specific fastening requirements.
Install Perimeter Sheets
For the required perimeter securement, position the 4 or 6 ft wide perimeter sheets over the substrate. Fasten the perimeter sheet according to the required number of fasteners for the project.
The project requires 12 in on-center fastening. Versico’s HPVX fastener plates must be used to fasten the Versa weld membrane to the deck.
Position the next perimeter sheet by overlapping the first perimeter sheet approximately 5 and 1/2 in. Fasten the perimeter sheet in the same manner as the first.
Utilizing an automatic heat welding machine, weld the two sheets together to achieve a minimum 1 and 1/2 in heat-welded splice.
Install Field Sheets
In the field of the roof, position the Versa weld membrane over the substrate whether using 8, 10, or 12 ft rolls.
When encountering penetrations, cut the membrane to fit as tight as possible around the units utilizing the pre-printed X markings along one edge of the sheet.
Install all of the required fasteners. The HPVX fasteners and plates are required for membrane securement. End lap splices are set at a minimum of 2 in to achieve a minimum 1 and 1/2 in weld.
No mechanical securement is required at this location. The sheets are typically fastened a maximum of 12 in on-center.
This project requires 12 in on-center fastening for the field sheets.
After the sheet has been fastened in place, position the next roll of membrane overlapping the adjoining sheet at least 5 and 1/2 in.
Remove the Gravel
The first thing we do with the gravel roof is get rid of the gravel. A lot of people want to tear the roofs off completely. I’m going to tell you that it’s really better not to do that because of landfill issues and all that. Also, you want to maintain your insulation. But when you go over this existing gravel, the real problem is weight. By removing the gravel, you’re getting rid of 200 lb per square. Our system is very light — only 40 lb per square — so we’re putting much less weight on the roof.
Here’s the gravel roof as we’re just starting it. It’s just a standard apartment. I’m going to let you look at the roof. We’re going to get rid of this gravel, and then I’m going to show you tomorrow that we’ll put down insulation and then put down the single-ply TPO system over the gravel.
Install Insulation and TPO
Next, after the roof is swept, we put this down — this is ½-inch insulation. This is basically a buffer so that nothing from underneath can get through if there’s a pebble there or anything. So this goes on the whole roof. Right now they’ve covered up most of it, and we’ll show you a little bit later what it looks like then.
Then this goes on — this is a small piece of it — but this is the TPO, 60-mil. It cannot be ripped; it’s very formidable. This stuff is supposed to last 50 years. If you’d like to learn more about this durable material and its proper installation, check out our complete TPO Roofing Guide. So if you can see in the picture, they’ve got about a third of the roof with the TPO on it. They haven’t started heat-welding yet, but I’m going to show you the heat-welding tomorrow when they start on that.
Adhering and Fastening the TPO
The next thing we do is show you how this gets adhered and fastened to the deck. Right here you have these screws and you have these wide plates — they’re about 8 inches apart all along every seam. The next row comes on top, and they heat-weld this. I’ll show you how we heat-weld this thing.
When it’s done, this weld is as strong as the material itself. The way it’s kept down is one side of the sheet is screwed down with these plates so the wind can’t blow it up. When the next sheet goes on, it’s stuck to the deck too — so the whole thing is properly secured.
Handling Pipes and Penetrations
Every pipe flashing and every penetration is dealt with individually by an installer. They heat-weld the way they’re doing it right there. Then they make a watertight boot around that particular vent. That one is square, so it has to be custom-made on the roof. If you pan over to this one, it’s a more standard circular one — those get heat-welded down too.
Your main concern is right around those flashings, so we do a very thorough job on that. Then this all gets a 50-year CLA on it and is clamped like a hose clamp in a car. That gets tightened down, so that seal is good for the life of the roof.
Edge Metal and Edge Detailing
This is what it looks like when it’s all done. This is a square vent — it’ll have a hood over it — so water cannot go in. Even if they missed a seal, it can easily be fixed after the fact. But we triple-check these.
Next, let’s talk about the edge metal because a lot of people ask me, “What do you do with the edges?” This is a piece of edge metal that’s got the TPO embedded in it so we can seal onto that. These connect with little pieces like this and are all heat-welded together. Then the material we put down first actually goes over the edge itself. This gets screwed down, then we roll a 10-inch sheet over it and heat-weld that too.
That’s how we do the edge.
Heat-Welding the TPO
We’re going to show you the heat-welder — this is a robotic heat-welder, and this machine is what does most of the seams on the roof. You see it there, moving back on its own. The installer is just keeping it steady and straight. That weld is airtight and watertight — close to perfect.
That’s basically the roof — how it gets heat-welded together. He just goes through this in about four hours. The whole roof is mostly done this way — only about 5% is handled with hand welders.
And that’s it — that’s our process for TPO over gravel!
Hello! I’m Abdullah, a passionate professional in the field of construction and roofing. I am the proud owner of SJ Roofing & Venting, a leading construction company based in New York. With years of hands-on experience, I write about various construction methods, techniques, and industry insights to share my knowledge and help others in the field. I’m also the founder and main contributor of this website.