9 Practical Steps about Joining Two Roofs with Different Pitches

Joining Two Roofs With Different Pitches

Joining two roofs with different pitches is a method that exists in the building and construction world. This technique is beneficial, particularly in home expansion.

If, by any chance, right now, you are looking for the information about how to join two roofs if they have different pitches, here we will share all the information we know with you.

As a starter, let us talk a bit about what roof pitch is.

What Is Roof Pitch?

Pitch is a very common part of roof construction. It often goes by the name of slope too.

If you want to know about the definition, it is the steepness of the roof. In simple words, we can say that it gives information about the measurement (in inches) of how the roof rises from the pitching point to the ridge in every standard 12-inch depth.

That is why when we talk about roof pitch, we also talk about a ratio range that we want to use. Something like this is usually shown in the range like 1/12, 2/12, 3/12, and so on.

roof pitch ratio and angles
roof pitch ratio and angles. image via roofgenius.com

The meaning of the ratio is easier to understand if you take a look at the picture above. It shows the image of roof pitch ratios, as well as the standard angles resulted.

As an example, please take a look at the 1/12 ratio image. The way to read it is like this. For every 12 inches length toward the ridge, the roof of the building rises 1 inch. With this ratio, the angle resulted is commonly 4.76°.

When to Join Two Roofs with Different Pitches?

There are some different cases we can find around us that make homeowners finally need to join the roofs that have different pitches. The most suitable example exists when a home expansion is necessary.

When you buy a new house, for example, with a specific budget range that you have, there is a possibility for you not to be able to get all the elements that you want in a living place. For example, there is no covered patio or screened porch available as an alternative spot for spending time when you are at home.

In a case like this, the best thing to do is to buy a house that has almost all the elements in your checklist. Later you can build the expansion you need once you buy the property.

A solution like this may result in the need for knowledge about how to join roof pitches that are not the same. The reason why we said so is that, possibly, it is enough for the expanded area to have a roof with lower pitches compared to the one that belongs to the original building.

A case like this is only an example. Some other reasons may apply, too, such as when you want to build an in-law addition or when you simply just want to make your house larger.

How to Join the Roof Pitches?

Now, it is time for you to know about how to join roofs, each with a different pitch. One thing that we want you to understand here is that the steps we want to share in this post may be suitable for some cases only since every house is different and possibly need some special treatments to join the roofs.

The sure thing is that we will try to elaborate on the general ideas so that you can imagine about how the process will go. Another sure thing is that this project is usually beneficial when you want to expand your house or add a new part to it, as we already told you earlier.

Do you know what that means? It means that here you will connect the new roof to the existing one. Read the following information to know about all the steps that you must follow.

Step 1 – Preparing the Area

When you want to join roofs in which the pitches are not in the same ratio, the very first thing that you must do is preparing the areas where the two elements will connect. Here we suggest you wear work gloves for safety sake.

an example of tool for shingle removal
an example of tool for shingle removal. image via homedepot.com

The way to prepare the areas is quite easy to follow. Here, you just need to remove the singles as well as the underlayment of each of the pitches. Of course, you do not have to strip everything down here.

Shingle and underlayment removal is only necessary around the connected area. The measurement that we suggest you follow is about 6 inches from the edges of the pitches.

This step will be easier for you to do if you use a tool. The only suitable item to use here is a shingle remover that you can find quite easily at a building and construction store. You can see the example in the picture above.

Step 2 – Measuring the Length of the Joined Area

When done with the first step, the next thing to do is measuring the length of the joined area where the two edges meet. In doing so, you just need to do the measurement along the roof edge.

Here, you should not forget to add approximately 12 inches to the length. For your info, all this will be the total length of the roof flashing, which is none other but one of the most critical items in a pitches-joining project as the one we talk about here.

an example of roof flashing material with 12-inch width and 25-feet length
an example of roof flashing material with 12-inch width and 25-feet length. image via homedepot.com

If you are not familiar with the name, roof flashing is a material which function is to direct water away so that it will not damage the roof, especially in some critical areas. Those include the parts where the plane meets dormer or wall surface and the surroundings of some features, such as skylights, vents, and also a chimney. Mainly for this post, the critical area is none other but the part where the two pitches meet.

Roof flashing usually comes in thin form. The material is quite varied, but the most common ones are galvanized-steel or aluminum. Both of them are the ones that professional roofers often use.

Step 3 – Prepare a Piece of Flashing Material

Prepare a piece of flashing material with a 12-inch width. After that, you can measure the length by using the size that you have got in the second step.

Mark the total length by using a permanent marker. Then, you can cut it by using metal snips.
The next thing to do is making a mark right in the center of the flashing along the whole length.

Step 4 – Place the Flashing on the Meeting Point

Next, you can place the flashing on the meeting point between the pitches of the roofs. Do not forget to slip the right flashing edge under the roof pitch. Here, you must choose the highest one instead of the lower one.

After that, you must prepare a 2×4 inches lumber, and then you can place it in the center position of the flashing along the whole length. This item will help bend the flashing to match the slope created by the meeting between the roof pitches.

The way to bend the material is quite easy. After you position the lumber, you can use its edge to bend the flashing. You must do everything slowly and gently until you can see that the right and left sides become suitable for the slope. When done, you can take the lumber away.

Step 5 – Sealing the Edges of The Roof with Lumber

Prepare two pieces of lumber with a 1×1 inches width. After that, cut each of them to fit the length of the joined area. The primary function of these two items is for sealing the edges of the roof.

Take a piece of the lumber and then slip it under the roof pitch that has a higher position. This way, you can find that the lumber edge becomes aligned with the roof edge. Besides, you will also see that the lumber position is now on the flashing material.

After you finish right there, you must hold the lumber in place so that you can apply butyl caulk on the upper and lower part of the piece along the whole length.

the use of butyl caulk in roofing
the use of butyl caulk in roofing. image via homedepot.com

If, by any chance, you do not know about what butyl caulk is, it is something that builders use for filling up the gaps that appear between building materials. Of course, it is also suitable to use in two roof pitches-joining project like the one we talk about here. It gets even better because butyl caulk can also keep away leaks in the roof area.

Step 6 – Apply a Bead of the Sealant Material

After you are done with the first lumber, you can move to the second one. Here, the first thing that you must do is placing the second piece on the pitch of the other roof. If you do it properly, you will see that both of the lumber edge and the roof edge becomes aligned, and the position is underneath the flashing, not on top of it.

When done, you will also use butyl caulk in the next step. Here, you must keep the lumber in place so that you can apply a bead of the sealant material along the bottom and top of the piece.

The next thing to do is allowing the butyl caulk to dry for an excellent result.

Step 7 – Securing the Flashing

The next step is securing the flashing so that it will stick perfectly to the roof. Here, you can use metal screws. The way to do it is by using a 6-inch space apart between the screws, all along the four edges of the flashing.

asphalt-saturated felt material for roofing.jpg
asphalt-saturated felt material for roofing.jpg. image via flickr.com

After that, you can prepare a piece of underlayment. Here, we suggest you use asphalt-saturated felt material.

Measure the size of the underlayment to have the same length as the joined area but 1-inch wider than the flashing. Next, you can place the underlayment right on top of the flashing.

Do not forget to slip its edges under the existed roof shingles. The last thing to do is securing it to the roof structure by using regular roofing nails.

Step 8 – Create a More Attractive Look

Next, you have to take care of the flashing to create a more attractive look. In this case, you possibly need to remove the trim of the roof’s eave temporarily for a smoother process. Later, you can install it back when everything is done.

As for the flashing, you can fold its edges that are located around the roof edges as well as along the bottom of the eave. You can use metal screws here to keep everything in place.

Step 9 – Cover the Flashing

The last but not least step that you must follow is using shingles that have the exact same appearance with the one existed on the roof to cover the flashing so later no one will even notice its existence.

In this step, you can start covering from the lowest up to the highest point. Here, usually, you will see some overlaps because you need to cover the roof entirely. If you want to make everything look perfect, you can try to do a trimming so that the new shingles can match the existed patterns on the roof.


Those are all the information we know about joining two roofs with different pitches. Maybe all the steps that we mentioned above seem easy to do.

However, before starting the project, we suggest you make that you really can do everything on your own. Besides, we also want you to realize your own building or particularly roofing skills.

We say something like this because a project to join two roofs like this is not only about the look. It is also about the result.

If you do everything correctly, then you will get the perfect result. However, if there is a mistake, there is a chance for you to meet some future problems later.

One of the most common ones is leaks that will lead to many other problems. An example is damages found on the roof structure that must you prepare a lot more money for the repair because when left untreated, you will only face a way worse trouble later.

Based on all those, please think carefully about whether or not you have the skill to do the project. If you feel that you are not capable of doing it, it is way better to hire a professional roofer to do everything for you. It is the wisest decision that can prevent you from using a way lot more money in the future.

So, hiring a roofer is still worth it to do. At first, you may think that it cost you more. However, at the end of the day, you will realize it as the right decision, particularly for you who do not have a good roofing skill.