Replacing a very old roof

I think my roof is probably close to 40 years old or more. I have no idea how many layers of shingles there may be. My question is does the decking have to be replaced? I have an estimate from one roofer that is to replace all the decking etc. I was all set to have him start when a friend came by and said that is ridiculous. He says you only replace it if it is bad. The roofer never said that it may not have to all be replaced. He said they replace it, period. Before I go and spend $10,000, I’d like to know if it is necessary. Thanks for any help!

If your most recent layer of shingles is at least 40 years old then my guess is that a whole new roof deck is a possibility. To put it as simple as possible, there are probably spaces of approx. one inch in between each of the boards under the shingles. With that amount of a gap in between each piece of wood, the shingles nail line would never land on every piece of wood.

I dont know if thats the scenario but I most likely find that one houses that have much older roofs and in certain neighborhoods. I always have to replace the deck otherwise the nails will have nothing to catch onto and I dont want to install in improperly.

Ask him why he needs to replace the deck. That should give you a simple enough answer.

Can you see in your attic to see what kind of decking is on there?or condition of it?

If your home is an older home, circa 1920-1930 or older, you may have and he may have observed that you have the spaced board decking, also known as, Skip Sheathing, which is Plank Boards installed with an approximate 1" to 2" gap in between each board, prior to a Cedar Shingle Roof having been installed as the first and bottom-most layer of roofing, with a minimum of one additional layer of asphalt shingles installed on top of that Cedar Layer.

Rather than guess, you should contact the roofing estimator who examined your home and roof and ask him the particular questions and don’t settle for anything less than straight truthful and comprehensive answers.

If the decking is old plywood sheathing, possibly when he walked on the roof surface, he noted a crunchy feeling, indicating that the existing decking was delaminating from either moisture and/or a lack of properly Balanced Intake And Exhaust Ventilation being present and if so, he should have included the modifications necessary to upgrade that to more than minimum standards.

How detailed was his proposal and did he take the time to sit down with you and explain all of the details and point out the features that he included and why?

If not, have him do that and also call around for another Roofers Opinion, rather than a neighbors opinion, who probably does not really know that much about long term roofing problems.


Ed’s advice is dead on. BTW , we call your neighbor a sidewalk superintendant. :stuck_out_tongue:

Good advice above, especially with having the roofer look at the underside of the roof from the attic.

Neighborly advice can only be good if their house is similar to yours, built at the same time, and if he has first-hand intimate knowledge of his roof that would apply to your house.

It wasn’t until I stripped off all three layers from my 45-year-old roof that I saw the 3/8" decking and could appreciate how soft it was. I could have left it on, but that’s not my style. Since I did it myself, I did it right with new 1/2" decking, which is now code. Sometimes I wish I’d’ve upgraded to a 5/8" decking, but it’s fine the way it is.

You are a very astute homeowner, I can tell you have been doing your homework and you have an understanding of roofing.I looked into Davinci for a customer, and never heard anything bad about it.That customer ended up choosing standing seam though, so I do not have first hand knowledge.I have installed US Tiles Shake version of that product.Its a good product as long as there is no foot traffic.Like ALL lightweight tiles, they are brittle. But , they are real clay, and should not fade.Good luck, and let us know what your final decision is.-Ray
PS…I do know that Davinci goes for $400 plus per square, which Ive always thought was expensive for a plastic roof.

There was some good advice given already, however, to answer your question, no! It is not necessary to replace the decking just because of how old or how long the shingles have been on the roof. On the other hand, the points others made about wood planks and sheathing may be valid. In general though, plywood replacement is something that is done as needed and is billed per square foot. Of course, if you are only doing spot deck replacement, the new plywood should span at least 3 joists and at least 12" wide. I generally don’t want anything less than a 1/4 sheet installed. Then again, you should also be wary of those that want to only replace full sheets because it is easier for them and they get to charge for 32 sq ft of deck replacement.

Why do contractors say replace the decking when in fact they are not replacing any decking but rather going over the old decking with new decking? Of course if there’s rot you will need to replace those boards but you still go over even the new boards with new decking.

I have found gaps large enough to warrant new decking on homes in the 40’s and a few in the 50’s. Most insurance companies I work with don’t bat an eye when I recommend installing new decking over the old. Most city inspectors easily put in writing that the new shingles need to be installed over a solid nailable deck surface.

The city of St. Paul is the most strict city in MN regarding deck gapping. From my experiance any gaps over 1/4 inch are considered too far apart and either need new decking over the top or detach and reset the deck boards so they are within 1/4 inch. Never done this but would be a an affordable option for home owners who cannot afford new decking.