Question: Load bearing walls and poured-wall basement

nanjJune 16, 2011

How are load-bearing walls on the interior of a house supported in a basement built with poured concrete walls? Posts and steel beams? Is this the typical, most cost-effective way?

The background to this question is: I am designing our home, playing off a Don Gardner plan and my sister is advising me. She has taken residential construction classes and GC'ed her own home and two additions to that home, and a total remodel of the original part - so, in other words, she is extremely knowledgeable! But she doesn't have experience with building on a poured wall foundation, only on a crawlspace.

In designing the finished, walk-out basement on our plan, she advises me that the walls in the basement HAVE to be in line with the load-bearing walls on the main floor to carry the load. I completely understand the concept and am not doubting that. But I thought that in a finished basement, the load is still carried by steel posts and beams, not by the studs in the walls. I thought that in finishing the basement's interior, the posts are either incorporated into the walls or are finished out as decorative columns.

Am I on the right track? My sister insists that the steel beams and posts is costly and will be one more thing driving up our already over-budget plan. In our current home which was completed when we bought it, the builder used engineered wood I-beams (forgotten the trade name for these) which I am guessing take the place of steel beams and posts. My sister insists that this method will be even more expensive.

(I've included a photo "borrowed" from the May post by ImaCurvyGrrl. I hope she doesn't mind!)

This is what I think of as the "typical" construction method for finished basements.

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A basement would be similar to a crawl space only taller.

If you don't mind your basement being divided up into rooms and a lot of continuous reinforced concrete footings to support the walls, you can use bearing walls with pressure preservative treated sole plates anchored to the slab. Don't assume that would be cheaper than beams, steel posts, and pad footings. Price it out.

If using beams they do not have to be steel; they could be built-up dimensioned lumber/LVL's or solid timber. The advantage of steel beams is that they are usually shorter in height for a given span and load and can therefore better fit under the joists and pipes can then pass over them.

The sizes and spans of steel or LVL beams are not prescribed in building codes and therefore usually have to be designed by an engineer so why not let the engineer design the whole system?

    Bookmark   June 16, 2011 at 9:06PM
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Ours is designed as your sister says - so we don't have any weird posts or columns. Instead, the rooms are divided so the load bearing walls mirror the upstairs. Not sure how this all came together but I do remember when meeting with our architect that some things had to be drawn a particular way so the walls would align. The benefit is that it does not feel or look like a basement - much better than the typical wrapped posts. I think if you are finishing it right off the bat you should be able to plan so as to not have any posts like the above picture, and that would be my preference!

    Bookmark   June 16, 2011 at 10:00PM
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A few points- Wherever you have load-bearing structures, whether columns or walls, you've got to reinforce the concrete slab with footers underneath. If you divide the basement into rooms, there are code rules about egress windows in the various rooms. I'd go with walls rather than posts myself. You can take your floor plan to a truss manufacturer, and they will design the floor joists and support necessary if you buy from them. Any 'real' lumberyard should offer this.

    Bookmark   June 17, 2011 at 6:15AM
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Epiarch Designs

building off of what renovator said, if you have load bearing walls on the first floor, you need to align structure below them in the basement. This can be beams or walls. Frame walls will be your cheapest option in most cases. However if you do not want a wall there, then price is not always the driving factor. However if you are a single story plus a basement, you shouldn't have too many first floor interior bearing walls.
If you use steel or LVL beams, they must be sized to carry the first floor load as well as the loads placed on the first floor (2nd floor and possibly roof loads). As you can guess, this can make wood beams, even built up, quite deep. Steel might be your best bet here if you have longer spans between columns in your basement to keep head room heights at ideal levels. I tend to disagree with the claim in wood costing more then steel. Steel will cost more then wood in most cases. The post can be hidden inside walls (why would you do this? save the money and make the wall bearing! unless of course you have a very high point load) or they can be boxed out and made decorative.
I joists should actually be cheaper then a floor truss, but typically cost a little more then solid 2x8-12 framing. However IMO, I joists are far superior. They can be had in very long spans so they can lay a continuous 30'+ joist across your load bearing beams/walls and allow for straighter and faster construction. Also, depending on the depth of them and the spacing, they can easily clear span 20'+. Plus they are a "greener" product.
Trusses will cost more, but the benefit you have there is the web openings to allow easy smaller duct runs and electrical access.

    Bookmark   June 17, 2011 at 10:00AM
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Thank you all for such great information. I know I can count on this forum!

I didn't know the details that you all gave, but I know that there are many ways to support a load - it boils down to what do you want the basement to look like and how much do you want to spend. I will have a professional do the actual construction drawings but I want to go into that step with as much knowledge as it takes to make informed decisions. Once I have the house design finalized, I might post it on the forum for comments if I decide my hide is thick enough!

    Bookmark   June 17, 2011 at 1:07PM
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Egress from a basement, regardless of the rooms, is by the interior stairway. Most codes also require an emergency escape and rescue opening from the basement as well as additional ones from bedrooms.

    Bookmark   June 17, 2011 at 2:50PM
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For my own home and for spec homes, I aim for the fewest posts possible. Consequently, I've never had more than four posts on two-storey homes up to 4,800 sf.

The pic above with eight posts in one corner strikes me as a dreadfully inefficient design. And that's even if they're buried in walls. As mentioned above, each post requires a concrete pier beneath. I've had building officials insist that these be as much as 4'x4'x4' Lots of extra hand digging, concrete and rebar.

An upper bearing wall does not have to transfer directly to a beam in the basement. That's why you hire a professional engineer to devise the most efficient and safe way to handle the loads.

    Bookmark   June 17, 2011 at 6:00PM
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Worthy, thank you for the information which helps with my construction knowledge.

    Bookmark   June 18, 2011 at 6:43PM
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Unless you can guarantee that the basement will always be as dry as the upper floors in all seasons I would not recommend using wood as a structural element within 4 ft of the basement slab. I have always used steel posts and LVL beams.

    Bookmark   June 18, 2011 at 8:27PM
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We hired a structural engineer to go through the architectural plan and spec out all the footings, foundation and framing throughout the house. After that, we just made sure the contractors followed those specs, and everything should be good. We made the basement as wide open as possible, with load bearing walls in only a few areas.

    Bookmark   June 21, 2011 at 9:39AM
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To compare the cost of bearing walls and beams you need to actually break the cost down rather than guess. Posts and beams only require double LVLs, a steel post, and a pad footing every 12 ft. or more. A 12 ft long bearing wall would need a pressure treated sole plate, a double top plate, about a dozen no.2 2x6 studs, headers at openings, mold resistant finishes and a continuous footing. Obviously the bearing wall would require considerably more labor.

If I had to guess, which I don't like to do, I would think the bearing wall would be more expensive than beams and would add no benefit to the house. If the owner wants basement rooms it would be better to put them where they are wanted and to be able to alter them later.

    Bookmark   June 21, 2011 at 10:09AM
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I used two Don Gardner plans, taking the main section from the Avery, with the master and guest rooms from the Clarkson. Since we are building in the same part of the country as DG is located, and our builder has used DG plans, I plan to send my drawings to DG and they will create the construction blueprints. I doubt that DG will spec out the foundation details you described, bdpeck. Our builder mainly builds churches (up to $30 million), doing a few houses here and there, so I trust that he will know the importance of engineering the design and direct us accordingly.

bdpeck, do you mind saying who engineered your plan? Since we will be building in the greater Charlotte area, a recommendation would be appreciated.

Renovator8, thank you for the details on considering load-bearing walls versus post and beam, etc. I have come to the conclusion that there is not an easy answer to my question. And I like the idea that not by not having all load-bearing walls, the basement lay-out could be changed in the future.

    Bookmark   June 21, 2011 at 6:01PM
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