How Many Layers of Roofing Are on my House?

There are a couple ways to determine how many layers are on your roof without tearing it up.

So you are thinking about a new roof and are wondering just how many roofs or layers you have up there. If you have an older home and you have not lived there for more than twenty years, it may be difficult to know the history of the roof. There are a couple of ways to get an idea without actually tearing up the roof to find out.

Let's say you know your older home was built in 1944. One way I start is to add 20 years to the year it was built and continue to the present. This gives me a kind of idea, of the worse scenario.

Example, 1944 1st roof + 20 = 1964 2nd roof + 20 = 1984 3rd roof + 20 = 2004 = 4 total layers, if it was never torn off and each roof lasted 20 years. This obviously is not the best way and only way to approach the inspection but will give you a rough idea.

Most codes now restrict more than two layers and with most roof coverings, codes only allow one roof. This does not mean the occupants of your home knew the codes. Here to the right is a roof that has seven total roofs. Six asphalt roofs over the original cedar shingle roof nailed to skip sheathing. { Photo provided by RoofersCoffeeShop® }

Now an attic inspection is needed. If possible lookup in the attic to see what the bottom of the roof looks like. This is called the roof sheathing and will help in figuring out, what you have. Most wood roofs were nailed on skip sheathing and this kind of roof can be seen at the skip. Cedar shake roofs use felt and so the black tar paper shows at the skip.

I have found most cedar shingle roofs will have at least one asphalt roof over the top before being totally removed. So in the case, if this home was built-in 1944 this plywood and roof were done in the early ’80s. Again doing the math this roof probably has two layers.

Most professionals like myself have many clues we look at to determine the age and layers of the projects we look at. I sometimes know just from the neighborhood I am in. This is important since it is a key factor in estimating a budget for a roofing proposal. Finding an extra layer of roofing can add several hundreds of dollars to a job. It is not a fun day when a surprise like this is discovered in the middle of a job.

You can get fooled if the edge of the wood roof was cut back 4 inches and removed, then a 1×4 was installed on the rake and eaves, then roofed over with asphalt shingles. This would completely hide the wood roof from the site and from the ground most likely not discovered till the asphalt roof was removed.  Many professionals have been fooled by this trick if accessing the roof was not done. This would be a major cost increase since the wood roof not only adds to the tear-off costs but now, the labor and materials to re-sheet the roof deck with plywood needs to be done.

The best way to find out the number of layers is to get up on the roof and walk on it. I can feel the layers under my feet. You must forensically disassemble a small area down to the roof deck. Then if the weather is a factor prior to the roofing project starting, a repair to that area should be done. This inspection should be done in a couple of areas on the roof because additions to a home or partial roof replacements mine have to be done.

This blog is about steep slope roof removals and should give you some ideas to help figure out how many layers of roofing you have on your roof. It is not perfect. I get fooled a couple of times every year and I do this for a living.

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