Expert: Richard Taylor, AIA - 1/15/2010

Question
Hi Mr. Taylor I have Couple of questions about building
1. Why is the most common width used for treads on stairs be 10 inches?
2. Why is a good idea to place windows on two exterior walls in a bedroom
3. Why is a a standard practice to leave 6" on each side of a door where it meets another wall?
4. What is a double top plate?
5. What is T.G. Plywood (subfloor)?
thanks
Emily

Answer
Good morning Emily, thanks for your questions!

The relationship between stair risers and treads is based on a formula developed many years ago.  Essentially it's 2(R) + 1T = 25".  That would make the riser 7.5" tall for a 10" tread, which is pretty typical.  Commercial building codes make the stair a bit less steep, with the maximum riser at 7" and minimum tread 11".  Residential codes vary, but the most common is 8.25" max R and 9" min T (pretty close to 25").

In any room, light is better distributed if it comes from more than one source (all the shadows don't go the same direction that way).  That applies to more than bedrooms, and it's not an absolute, but it one of many good rules of thumb.

Most homes have trim on the jambs of doors, and 6" leaves room for the trim and a little space for drywall.

The double top plate is part of a framing system called Western Platform; the double top plate is at the top of bearing walls to distribute the loading from the floor above evenly.  It's usually 2 stud members stacked.

TG is really "T & G" and means "Tongue and Groove".  The edges of plywood used for floor decks are shaped to fit together - the tongue fits in the groove - so the sheets interlock for a stronger floor system.

Hope this helps,

Richard Taylor, AIA
www.rtastudio.com
www.rtastudio.blogspot.com
www.rtaplans.com