Decks/Deck Stairs


Deck Stairs
Deck Stairs  
QUESTION: I am planning on replacing my wood decking with Trex and have a question regarding the stairs.  Attached is a picture of the stairs.  The tread is 36" wide, with the posts and balusters mounted on the outside of the skirt board.  Mounted flush on the inside of each skirt board are the stringers, which can't be seen from the picture.  They are 14 step stringers, quite a long run. My plan is to duplicate this stair construction when I install the Trex stairs, with the railings mounted on the inside as spec'd by the manufacturer.  I do not currently have support posts at the midpoint of the wooden stairs.  Is this going to be a problem when I replace it with Trex?  My understanding is that composite is heavier than wood.  Would the stringers and skirt boards provide enough support for the length of the stairs without having to consider adding support posts?  Thanks so much.

ANSWER:      So, a few quick questions, so that I may understand more clearly...
    You are saying that there are existing "cut to shape" stringers in addition to the "skirt boards". What size boards are these all...2x10 or 2x12?
    Keep in mind that composite decking in a 5/4 x 6 size, generally requires a maximum 16" o.c. support spacing.
    What type and material of railing are you thinking about using?

---------- FOLLOW-UP ----------

Stringer 1
Stringer 1  

Stringer 2
Stringer 2  
QUESTION: Hi there.  Yes, there are 2 existing cut to shape stringers in addition to the skirt boards (see two attached images).  They are 2x12.  I believe Trex recommends the stringers to be 12" o.c.  So, my plan is to install 4 stringers 12" o.c. and add the skirt boards for added support.  The railings will be standard Trex Select composite material.  Thanks.

    Well, normally, I would say to go ahead and construct the stairs that way, build your railings, and then add support as deemed necessary. Since you are to be using Trex decking, which is very flexible, and Trex composite railings, which will not provide any strength, I'd say that you are most likely going to have to add 2 posts and a girder about halfway down the span of the stringers. You may have to add some other components as well.
    A wood railing, for example, can actually add a great deal of strength and rigidity to a set of stairs, acting like a suspension bridge in a way. A railing made from composite materials,normally has the opposite effect to a deck or set of stairs. It not only fails to *add* strength, but requires much more support for itself. It is also generally much heavier than wood.
    Personally, I'm not a fan of anything Trex, nor use of composite for railings. A Trex made composite railing is a double whammy...but that's just my opinion. I suppose virtually anything can be made strong if done correctly and with much attention to detail.


All Answers

Answers by Expert:

Ask Experts


Michael Romano


I can answer any questions relating to decks, porches, exterior stairs & railings, walkways, access ramps, pergolas, deck roofs, screen rooms, etc... These may include design ideas, footing to framing design & construction methods, various species of woods vs. composites & pvc/vinyl materials for decking, skirting, or railing applications. I also have expertise in various rain-free systems for under-deck storage & living spaces.


I have designed and built decks and many other types of outdoor structures for over 25 years for my own home improvement company. We also perform many other types of home improvements, including window & door installation, molding & trimwork, siding, basement finishing, siding, etc. Our main love however, is decks!

NADRA - The North American Deck and Railing Association. Several Small Business & Home Improvement Contractor Alliances & Associations.

I have written several articles over the years for,, and many other deck & construction related websites.

High School graduate. 2 years of Mechanical Drawing & Architecture classes. Vocational School graduate. 2 years of Construction Technology & Carpentry classes. Many years of reading, researching, and application in the real world.

Awards and Honors
I am certified by several decking manufacturers for expert application & installation of their products.

Past/Present Clients
Mainly local residential clients, and occasional commercial clients, including restaurants, nightclubs, office buildings, etc.

©2017 All rights reserved.