4

I'd be using stainless steel deck screws or stainless steel lag screws.


2

Think about replacing the sill and the casing with some of the PVC or composition boards that are available in the home stores. Any wood you put down there will be rotten again in 5 years.


1

In my humble opinion, nails have little purpose in construction of a deck. There are at least five different types of screws made specifically for this application. They have torx heads and are very solid. Only specific instructions I would otherwise have is that if you really want to press the old and the new sisters together, drill a pilot hole in the side ...


1

Adding a sealer to the surface does not sound like a permanent repair - may last a few seasons... Covering the whole roof again does not sound like a reliable solution. Will this treatment do the 70years the original surface did? I would look at opening that joint by removing the rivets / screws whatever the fixing is, then re-doing that seal and refixing ...


1

It’s part of the weather-tight system. It’s not designed to STOP moisture, but rather CHANNEL moisture that may enter during a sever storm. Rather than have beads of water laying along the edge, the plastic cover will channel the moisture to a drip edge on the skylight. I agree with @J. Raefield, glue it back in place and make sure the edges are sealed.


1

Nothing on the inside like that would have any purpose related to water entry; if the water got that far in, there would already be damage. That is, at best, just draft and heat loss, but most likely it's just cosmetic. I would just glue it back in place.


1

I'll tell you what I did with my deck and it worked great... The product name is Copper Green-Brown Copper-Green 1 gal. Wood Preservative https://www.homedepot.com/p/Copper-Green-1-gal-Wood-Preservative-221832/300502828 I just retreat it every 3 years ( no stripping needed ) and it looks fantastic. Very simple solution 👌👍


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