Can somemone please help. When I went to the lumber yeard and asked for the 4 by 8 by 24 Beams (2) (P.T. pressuer treated) they did not know what these were as they were not available. I got the same answer from Lowes. Is there a substitute and what are they used for
and if not where can I get these and at whatcost? Thanks
Yes, you don't want to have a single beam that long - it is very difficult to find and install. You can get shorter material and join them over a pier support where you can nail into both beams and strap them together.
Alternatively you can build up a beam out of smaller material. You could use 3 PT 2x8's as shown here: http://www.countryplans.com/builtupbeam.html (then you wouldn't need the plywood).
That would have a width of 4-1/2". Check your pier bracket or saddle and see if that size will work for you.
I think that most brackets are made for 4" (actual 3-1/2") or 6" (actual 5-1/2"). You could either use 1" PT (deck boards) in your beam make up, or two layers of 1/2 ply (independent between 2X materia) or use PT spacers at the same location of the brackets making sure that you orient all the spacers on one side to keep beam alaignment. They do make PT 4X6 but as John stated will not work as well for your application and would probably not be a strong as a make up beam.
Also, you may not need to use PT material if it will not be in contact with the ground or exposed to moisture. The usual reading is material within 6" of the soil needs to be decay resistant.
Code check :D
Treated is required if < 18" to ground for joists or <12" for girders.
I was pretty sure I would not be able to lift 4 x 8 x 24' PT beams into place by myself, so I asked for 4 12's. Good thing, they were heavy enough.
This is what I did.
(https://i282.photobucket.com/albums/kk265/considerations/strapping.jpg)
Right Don_P
Those are also the Min. distances to have for a crawlspace where you can work on it from below.
(http://www.mtnhighinspections.com/sitebuildercontent/sitebuilderpictures/.pond/distance-to-soil.jpg.w300h190.jpg)
I was thinking of the distance to exterior untreated wood such as siding.
(http://www.naffainc.com/x/cb2/Wood/6%20inch%20wood-to%20earth%20separation.gif)