7 Tips To Avoid Skylight Roof Leaks

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tips on installing a skylight diy

Here is expert advise on how to complete your skylight installation so that your unit is durable and leak free. In fact, skylight waterproofing is one of the most challenging parts on the job and requires some technical knowledge.

Our pros share their secrets for homeowners who want to know how to install a skylight by themselves.

1. Select the RIGHT mounting option

When it comes to mounting your skylight on the roof, you will have three options. It is important to understand the difference between them prior to selecting your unit, as this will directly affect the total cost and the complexity of the installation.

•Flush-mounted: is generally easier to install in new construction, than as an afterthought. Units are often a simple and inexpensive acrylic dome.

•Curb-mounted: is elevated off the roof surface by a ‘curb’, which is constructed by the installer. Experience in curb construction and skylight mounting is essential to assure proper fit.

•Self-curbing: sometimes referred to as a self-flashing skylight. This is a premier mounting method, as it comes with the curb already constructed to perfectly fit your unit. Skylight flashing is pre-installed for the easiest and most trouble-free mounting.

2. Consider your roof pitch

The pitch of the roof where your skylight is located will affect the amount of sun heat entering the interior space. The steeper the pitch, the greater the heat gain.

It is optimal for the skylight slope to be 5 to 15 degrees greater than the geographical latitude of your location.

ALL steep slope skylights require a minimum roof pitch of 3/12.

3. Ensure proper roof ventilation

Skylight in a Modern Living Room

Condensation on your skylight can be an issue if there is no proper ventilation in your home, or in the room where it is located. This is a major concern for bathrooms. For this reason, you might consider buying an operable skylight rather than a fixed one.

On the other hand, you may find that opening and closing a skylight for ventilation purposes may be more trouble than it’s worth, and decide not to install it. You can avoid this problem by purchasing an expensive electronically operable model. Prices for an operable skylight start at around $1,100

Another option that is more budget friendly is to have ventilation fans installed in the room, to keep the humidity from becoming too high.

4. Best skylight roofing materials to use

Asphalt Shingle Roof With Skylight

Wood, asphalt shingles, concrete tile and slate are all skylight friendly roof systems. Many people wonder if you can put skylights in a metal roof. Its a complex situation, but in short the answer is: yes you can, if you have metal shingles. However, if you have a standing seam roof, or any other corrugated metal panels system, it will not be very well suited for a leak-free install.

Due to these systems’ design, the back pan of skylight flashing (which receives 99% of all water during rains) is reliant on sealant to remain watertight. Also, barrel roof tiles, whether made from metal or clay will have similar problems.

Therefore, if you plan to have skylights installed on any of these roofs, you should avoid doing this yourself, unless you have a lot of experience. Moreover, we strongly recommend you choose your installer very carefully, to be sure that the work is done correctly. Otherwise, you run a high risk of constant leaks.

5. Don’t try save money if hiring a pro

Not so long ago, it was thought that a skylight roof will inevitably leak, and therefore installing skylights should be avoided. In reality, recent technological advancements have enabled manufacturers to greatly improve the quality of skylight design, which together with better flashing methods makes the unit impervious to water penetration. Many manufactures, such as Velux, even offer a 10 year warranty against leakage.

However, to have a leak free-service life, very precise, high quality installation is a MUST. A poorly executed job can still render even the best quality skylight susceptible to water infiltration.

It is very important for the roofer to always follow the manufacturer’s specifications. These will often include instructions about mounting the skylight above the roof surface on a curb with properly installed flashing, and waterproofing to send the water away from the unit itself.

Not every roofer knows how to install a sklylight correctly or has enough experience to do it well. Don’t try to save a few hundred bucks by hiring a contractor without the necessary technical knowledge and expertise. It will cost you a lot more money and trouble when you need to repair a leaking roof.

We recommend getting a few quotes from local pros and hiring someone who can provide good references from similar completed jobs.

6. Technical limitations to keep in mind

Skylight in Roof Valley

Skylight in Roof Valley

While having skylights in your roof is great, sometimes you cannot add them in certain situations / placements, as it will cause leaks.

Examples of such placements are:

– Roof Valleys / Hips
– Installing skylights too close to the eaves
– Not having enough roof pitch – flat roof skylights often have leakage problems.
– Adding skylights to existing standing seam metal roofs, etc.

All of the above can lead to water infiltration and will diminish roof system integrity. Consult your roofer about proper placement for skylights, and also get a second opinion if possible.

As a rule of thumb, don’t install skylights if you encounter any of the above conditions!

However, if you do add a skylight near a valley, hip or roof pitch change, place your unit at least 3 feet away from such conditions. This will help maintain your roof’s integrity and prevent leaks!

Moreover, avoid putting regular skylights on roofs with slope less that 3 in 12, without building a curb.

I once did a job on a 1/12 pitch shed dormer roof, where the builder installed 2/12 sloped curbs and installed skylights (see below).

I told the owner that the VELUX skylights they used required at least 3/12, and if left as is, the warranty would be null and void, as well as pose a high likelihood of leaks.

She made the builder take out all the skylights and raise the curbs to 3/12. Now, she is enjoying a leak – free roof and a beautiful view!

Lastly, you should not add skylights to an existing standing seam roof. Since the panels are attached so they cannot be removed, if you start adding penetrations, the roof WILL leak, and you will not be able to properly flash the skylight.



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This roofing guide is presented by Leo B.

I've been a roofer for 15 years, and specialize in Metal Roofing and Flat Roofing.

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2 comments on “7 Tips To Avoid Skylight Roof Leaks

  1. We are now having our new house constructed as our old house has been already sold. Our contractor has been asking as to what type of roofing should I prefer to install, that is why I am searching for it online. I am so grateful that I’ve just found your these useful tips. I am now discussing it with him if I’ll ensure that a proper roof ventilation will be installed, thanks a lot!

  2. Thank you for the help. My wife and I are going to do some remodeling and would like to install a couple of skylights. I definitely want to avoid future leaks, as you warned.