How do I find a leak in attached garage Ask Rick

I’ve got a leak in attached garage but can’t find where it’s coming from. How can I find it the shingles look OK and are all in place.

sugarland, Thanks for your question. Roof leaks can be very difficult to find if they are not obvious in the first place. If there is a leak in the attic, then of course water is somewhere getting in either through the roofing shingles, a vent, in a valley or through a nail pop etc. So, it takes a bit of investigation to be able to figure it out yourself.

The first thing to do is to walk the roof, if you feel safe doing so. If the roof is very steep, you may need to get a pro to look at it. You will need to look it over very carefully and take your time doing so. Look at the shingles to see if possibly tab is missing or cracked. Look to see if there are shingles that seem to be raised up a little off the roof in comparison to the other shingles. This could indicate that a nail popped up under the shingle which creates a small opening around the nail where water can run in. Really take your time when doing this.

Nail pops can be repaired. You can lift the tab and carefully remove the nail with a flat bar or nail puller. Then install a new roofing nail a couple of inches away from the one you took out under the tab. Make sure to then use a good silicone based roofing cement to caulk around and over the nail head and Lay the shingle tab back down. If you accidentally break of the tab, then you will need to replace the shingle.

If you do happen to find shingles missing or cracked, then you need to replace them. If you have some extra shingles that you kept when the roof was put on, then you are in good shape. However, if you do not, then you will have to try to get the best match you can to fill it in.

Many good roofers I know, will remove a good existing shingle from somewhere on the roof that is out of sight, and replace it with a new shingle that is not quite a perfect match, and then fill in the damaged or missing shingle with the existing shingle removed from the other part of the roof so that the match is better where it can be seen more.

When you get a nail pop under a shingle, it can be one of two things. It can be the nail that was used to fasten the shingles to the roof or it can even be a nail that was used to attach the sheathing (Plywood or OSB Board) to the roof that has come loose from the roof rafters or trusses. To help determine this, you can go into the attic with a light or bright flash light, and look at the bottom of the sheathing where it is nailed down over the rafters or trusses.

Sometimes you will notice that a nail or possible several nails in a row have just barely skimmed the edge of the rafter when the plywood was installed. If this is the case, it would explain why the nails are popping up.

When looking at this, notice to see if it looks like there are any larger gaps between the plywood and sheathing where the sheathing looks like it may have raised up off the rafters. If that is the case then the nail may have come loose in the area and popped up on the roof causing a place for water to get in.

You may also notice water stains on the underside of the plywood and on the the rafters or trusses themselves. Water can also come in through an area and run down the rafter and then leak into the ceiling or wall when if fact the leak occurs higher up on the roof. So, look this over and become a leak detective to try and determine both the source of the leak and where the water is actually coming in.

If the leaks seem to be happening more when there is ice and snow on the roof, you could have an ice damming problem. Click on the following link to find out more about this common problem.

With this, it is very important to make sure the valleys of the roof and the perimeter of the roof where ice and snow tend to build up, have ice and water shield under the shingles and installed properly to help prevent water penetration. You should also make sure the valley shingles are not broken and have too wide of a separation. Sometimes the improper installation of shingles in the valleys will be the very thing that causes the water leak.

Some roofers will lace the shingles in the valley, others will install metal up the valleys and then do a straight cut on the shingles. And, you will find that they both have their reasons for doing it that their way. However, if you have ice and water shield properly installed in the valley, then either method, will work, if again, installed the right way.

Other things that can cause leaks are flashing that is not installed properly or that has come loose around chimneys, skylights, plumbing vents, roof vents or where the roof meets the side wall of another part of your home. Flashing needs to be properly installed and sealed.

Of course you could have even more problems if the roof sheathing is rotted and needs replaced or if you have more then two layers of shingles on the roof, or if the shingles are just old and need replaced.

In many states the building code permits you to install a second layer of shingles over an old layer of shingles. Sometimes the original layer of shingles can curl and cause the new layer of shingles to follow suit and if this happens then you can have all kinds of problems and leaks. Nail pops can become more prevalent.

So do the outside and inside inspections in a very precise manner. Inspect sections of the roof at a time and do the same inside the attic. Remember you need to have bright light when inspecting the underside of the roofing in the attic and you also need to do this with caution since you may be walking directly over the ceiling joists or rafters if you don’t have a walkway to walk on.

There is a test you can do as well that might be able to simulate the leak. Take a garden hose up onto the roof and have someone on the ground turn the hose on. Spray the water over any areas of the roof that you suspect may be the cause of the leak and then have the person on the ground check to see if and when the water starts to leak inside. Make sure to watch the area or areas where you have noticed the water leaking in.

Do this around all the flashed areas as well and in the valleys. Spray the water in different directions and let it run down over areas you may suspect. By doing this you will be able to simulate different types of rain patterns that can cause the water leak problems. If you are successful in finding the leaks by using this method, they the repairs will be that much easier for you.

If you see the water leaking into the room where the leak or leaks you discovered before occurred, then go back up into the attic to determine on the location on the underside of the sheathing and on the rafters, where the water is entering and where it is running to when it gets into the garage below. If this works, then you can determine what needs to be repaired to stop the leak.

If you feel you are not capable of doing this yourself, or if you feel safety is an issue for you, then contact a professional to come out and give you a free inspection/estimate.

I hope this helps, Rick

Rick Maselli is Founder and Editor of and Ask Rick

Leave a Reply