I planning on adding a room on the back
of my house and I have bought some books, but I'm still confused on a
couple of things.
1. If you pour a concrete foundation
wall is it necessary to have beams to
support the floor joist. And what is
the best method of attaching the joist
or beams to the concret wall?
2. Should the footer and concrete
wall be poured at the same time, or
done in stages with rebar to ajoin them?
Wood vs. Poured Concrete Foundations
Summary:
Poured wall foundations and wood
can coexist together for a beautiful finished basement. Poured wall foundations
provide permanence that wood foundations sometimes do not. The wood can be used
for the floor trusses with wood I joists that span large distances without
structural beams in your basement.
DEAR TIM: Please shed some light on the advantages on a wood foundation or poured wall foundation. We plan to build and I want a poured wall, but my wife's boss has a new home with a wood foundation and he has convinced her it is the best option. I admit their finished basement is super without posts but question the strength and durability. We hope to start building in February. My son who is a framer agrees with her. William D. Caldwell, Oregon, OH
DEAR WILLIAM: The simple answer is why not have both and an additional insulation system thrown in at the same time? What would you say if I told you a poured concrete foundation that had integral wood framing as well as closed cell foam could be erected at your jobsite in just one day? Would you be impressed if your son started to work the next morning installing prefabricated floor trusses that could span 30, 40 even 50 feet with no center support beams? It is okay, you can get up off the floor now.
My college degree is in geology and I have a special interest in history. When I look back at the Seven Wonders of the World and see the ones still standing, they are not made of wood. I love wood and my house contains lots of it, but I refused to use it for my foundation. I know structural engineers can easily design a wood foundation that will withstand all of the static and dynamic loads thrust upon it by soil and even additional pressure from uphill soil sliding down towards a wood foundation. But I desire the permanence of steel reinforced concrete which is nothing more than artificial rock.
This CCA-treated-lumber post was rated for burial. That means it was protected against decay from wood rot and insects. As you can see, something went terribly wrong. The post was only in the ground for 15 years. Imagine if this happened to your wood foundation. PHOTO CREDIT: Tim Carter
As for wood foundations, what happens if the day the lumber was scheduled for treatment the worker at the plant in charge of injecting the chemicals had a fight with his wife or his boss and had a severe head cold at the same time? Is it possible the wood might not get treated with enough chemicals? Sure it is possible. Is it likely with modern quality controls? Probably not. The same can be said for concrete. Your builder may order 3,500 PSI concrete, but the ready mix plant may ship a lower strength product.
But with concrete, an experienced concrete mason can actually look and work with concrete coming out of the truck and have a very good feeling as to the amount of cement in the mix. Higher strength concretes have a completely different look than low-strength mixes. You can't say that about treated lumber.
You are in luck as you have a precast concrete foundation plant within 35 miles of your home. These foundations are ideal for any number of reasons and the best part is they are poured in climate-controlled settings and then allowed to cure in rooms where the temperature does not drop below freezing. Once the panels are cured, they are trucked to the jobsite and dropped into position with a crane. Where two foundation panels meet, the seams are permanently sealed as each panel is bolted to the adjacent one. Once the complete foundation is set, the exterior is coated as any foundation would be with a true waterproofing compound.
Talk to a good residential structural engineer about your floor system. Let this person design a superb subfloor system using floor trusses or possibly wood I joists. Wood Floor trusses and some wood I joists can be made to span incredible distances with no center beams or columns. What's more, if designed properly your floors will have no spring to them at all. They will be as stiff and hard as Chinese arithmetic!
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Comments:Welcome! I, Tim
Carter, don't answer questions
here. If you post a question here in the Comments Area,
perhaps another visitor will help you. You need to go to the Ask
Tim page if you want a question answered. Once there, look
closely at how many weeks behind we are. Please be patient as you use
this free service. If you have an emergency and need to talk to me,
there is an option there for you.
Garry Lankford 01 Feb 2008, 15:21
AsktheBuilder 01 Feb 2008, 15:27
Garry,
The joists normally are fastened to a treated-lumber sill plate that is bolted to the foundation. Beams typically rest in beam pockets. Footers are poured first with a key way and rods that stick up to help make the connection.
mark horning 17 Mar 2008, 19:14
You are a very ignorant man in this subject and obviously have no business
answering questions about wood foundations. This is a perfect example on
how the internet can be dangerous. You should try some research before you
give you expert opinion. Try the U.S. dept. of agriculture.
AsktheBuilder 20 Mar 2008, 08:40
Mark,
You are absolutely entitled to your opinion, but in this case, you are wrong. I will, however, give you the benefit of the doubt. I say this because the photo in the column above was not in this particular column when you wrote your comment to me. That post was buried by me about 17 years ago as part of a playset I built for my kids. I purchased the highest-quality treated lumber for the job. The playset was taken apart two years ago so I could build an outdoor shed. You can imagine my shock when I pulled that post from the ground. Yo can clearly see the part of the post that was above ground. It has no visible surface damage. That photograph has not been altered, and I have that exact piece of wood in my possession should you wish to examine it. As for the US Government being the center of the vortex of accurate information about this topic, I think that is debatable.
Ragman 15 Jun 2008, 16:34
I can top that. I just replaced two treated fence posts that were termite
infested and rotted after less than 8 years. Needless to say they were
replaced with metal posts.
steven lasater 16 Jul 2008, 09:51
how do i choose between concrete and peer and beam foundations. in the area
i want to build. does the ground ,weather snowfall etc. matter??
Richard Berg 28 Aug 2008, 22:07
I have built several wood basements and if the wood ever gets wet one time
then it was built incorrectly. Wood basements should be 2x8's spaced every
12" with 1" of plywood applied over that, (all construction nailed with
stainless steel nails) then 2 sheets of 6 mil visqueen (plastic),(only
nailed at the top) than 1/2" blue down( only nailed at the top) then 1-2 ft
of stone backfilled around it. There must be stone underneath the wall or a
concrete footer with a foam sill sealer between the bottom plate and the
concrete. Stone also under concrete footer.There also must be a tile around
the perimeter of the foundation than drains into a sump pit. In my own
house I have a wood floor in my basement and it is awesome. This is just
the basics, and I would never have a poured concrete basement in place of a
wood basement . If done correctly they will outlast a concrete wall and you
will never have a damp basement. Some on this site have no clue what they
are talking about. I have been a carpenter for thirty years and have never
seen a wood basement fail if done correctly but have seen scores of
concrete basements fail and the ones that don't are still miserable to be
in. You wont feel like your in a cave with a wood basement. Email me if you
like and I will send you a detailed plan of how a wood basement should be
built.
Darren Richard 10 Sep 2008, 21:37
I have a home I am building in a rural environment where the concrete walls
are already in place but I am considering a wood floor instead of a
concrete one.
So far this website is the only one I have been able to find that discusses the issue rather then being focused on hardwood floors being installed on concrete. Is anybody aware of any resource on the internet that I could access to assist in the design of my floor?
Frank 12 Sep 2008, 10:08
Tim,
I believe your analysis of a buried timber as a proxy for the performance of wood foundation is off-base. If you understood the wood foundation system you would recognize that the foundations are not just buried in the dirt as you would a playset timber. (Just the same as houses are not just thrown in a hole.) For any foundation to be dry you need proper backfilling and grading, gutters, etc. to avoid water. The beauty of the wood foundations is that the gravel base and careful backfilling, 6 mil poly, drainboard allow all water to drain away from the foundation without impregnating the wood.
Rick 28 Sep 2008, 11:06
Not to mention the fact that basic treated lumber is often not certified
for use as foundation building material. The lumber must bear an
appropriate certification agency logo and standard number. These facilities
specialize in treating lumber specifically for use as foundations and have
been approved as treating the lumber correctly. Standard junk treated
lumber is not the same in most cases thus probably another leading factor
as to why your post failed on top of the drainage and exposure issues.
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