How to find the studs on the ceiling through 4.5″ of polyiso

atticjoistslocating

I am starting to install polyiso on the interior of my slanted cathedral roof assembly and am having trouble finding the studs through the 4.5" of polyiso that I have.
Things working against me:

not all studs are perfectly 16" OC.
The ceiling deck is at an angle.
When I place the screws in it's hard to get them into the studs or even find the studs with the angle of the ceiling.

Are there any videos or techniques that can help me find the studs…I'm at a loss here!

Best Answer

Never installed polyiso but if I was presented this issue this is what I would do.

I would go one sheet of polyiso at a time and find the studs on the ceiling before I put the polyiso up. Measure the distance of the studs from the edge of where the polyiso will be stalled and then mark the polyiso with those messurements. Use a chalk line to give a nice straight line where the studs will be on the polyiso. Installing will be simpler this way.

Everybody wants to save money

Builders and utility companies are not in the business of wasting money, which means the main line will be as straight and as short as possible. This is a big help to you, since it will narrow your search. Walk out to the curb shut off, and look back at your house. Try to determine the straightest, shortest path between the curb shutoff and the house. Now you'll have a general idea of where the line enters the home.

Trace the line

In most cases utilities bury a tracer wire in the trench above utility lines, to make the lines are easier to locate later. If you call 811 (assuming you are in the US, though I believe this service is offered in other areas as well), they should be able to send somebody out to locate the line for you. This will show you the approximate path the line takes to the house.

Don't let pipes freeze

Because it's a water line, it will likely enter your house below the frost line. If you can determine the frost depth in your area, you'll have a more targeted area to search.

People are idiots

It's not uncommon for people to do dumb things, especially when they don't know how dumb they are. Water meters and shutoffs are ugly, and nobody wants them in their newly remodeled living space. It's possible that your valve has been walled up, and you'll have to remove some finish material to find it. Look in closets, and keep an eye out for access panels.

If only you had X-ray eyes

There are a few tools that can help you search a wall where you suspect the valve might be. A stud finder should be able to locate pipes in the walls, depending on the stud finder you buy. A metal detector will find anything metal, so that could also come in handy. If you've got a bunch of cash to throw around, a thermal camera may be able to actually see the pipe through the wall.

Where does service enter?

After reading the update to the question, and then reading through building code. It seems that it may be possible that there is not a shutoff valve where the line enters the building.

International Residential Code 2009
P2903.9.1 Service valve. Each dwelling unit shall be provided with an accessible main shutoff valve near the entrance of the water service. The valve shall be of a full-open type having nominal restriction to flow, with provision for drainage such as a bleed orifice or installation of a separate drain valve. Additionally, the water service shall be valved at the curb or property line in accordance with local requirements.

According to this, there must be a shutoff valve "near the entrance of the service". However, in most cases the water meter has to be near the "entrance of the service" too. In your case, it may be that the "entrance of the service" is at the property line, and not at the building. So there may actually be no shutoff valve inside the house.

Drywall – How to locate studs in the wall

The studs will likely be at 16" intervals from a corner, but that corner could be the corner of the building and not the room if you have a wall T'd with another wall. The first 16" could also be more like 15" depending on how the walls are laid out. There are several places you can check to give you more hints:

The first, and easiest is any outlets and switches. They should be attached to a stud in new construction.
The next is any trim around the floor or molding around the ceiling, which should be nailed at the studs. You may be able to see small bumps from any nail filler on these.
And the last method I can think of is to use a light at a sharp angle to see if you can notice bulges in the drywall at 8' intervals. Those are the non-beveled edges at the end of the drywall, and you should be able to notice them if the drywall was installed horizontally (frequently done, but not always).

Beyond those non-destructive options, and the stud finder that you've tried using, you're left with drilling test holes. I'd suggest making the holes close to the floor where they will be less obvious, but not so close that you're hitting the base plate of the wall (you need to be about 2" up).