Should I use treated timber?

[The Medway Handyman]

Had a job last week to remove & rebuild a small deck.

Second photo shows how they first realised there was a problem. Second photo is what I found underneath.

the deck was installed by the house builder from new about 9 years ago.

[Lobster]

Yes, but what does the second photo show? ;-)

David

[Geo]

Looks like it was treated timber but they trimmed the ends to fit the joists and the boards then rotted from the untreated cut ends?

[The Medway Handyman]

Some of the boards had rotted all along their length and some of the loists. Also laid with no appreciable gap between boards.