Built-in Over Concrete Foundation

[Jonathan McCully]

Hey guys. Been awhile since I’ve been active on here, but anytime I have woodworking questions, I know this is my best place to turn for answers. Glad to still see you all here.

I'm planning a remodel of my office at home. Going to rip up the carpet which is laid directly on the concrete slab (with some carpet pad) and install a built-in bookcase and hardwood floors. My questions is regarding the bookcase. Would you install that directly onto the concrete with some moisture barrier underneath accounting for the height of the hardwood flooring or put some plywood down and build onto that? Most of the videos and resources I’m finding generally are building over flooring or subfloor, not concrete. It seems best to me to do the built-in before the flooring to reduce the amount of flooring needed and to accurately cut the flooring up to the edge of the bookcase. I’d welcome any thoughts you guys have.

[Coop]

Hey Jonathan, welcome back. I think either option would work. I have two friends that one,  recently replaced an under counter ice maker and the other, a clothes washer. Both had installed hardwood flooring after the old appliances were installed and both had to demo the flooring around the old ones to get the new ones in. Replacing your bookcase will probably not be an issue. If the bookcase is sizable and the saving on flooring materials are substantial, then I would floor around the bookcase. If you foresee this office becoming something like a babies nursery in the future and the bookcase not needed, then I would install the flooring first and build on top of it. 

[fcschoenthal]

+1 on installing over flooring. 

[Chestnut]

I'd do flooring first and bookcase on top. If you wanted to save the flooring and know the future isn't an issue, I'd still recommend some sort of vapor barrier and plywood etc to separate the bookcase from the concrete.

[wtnhighlander]

Adding a built-in over a non-concrete substrate give you a little wiggle room to adjust the fit. It is much easier to chisel out a tight spot in the plywood or flooring, than solid concrete.

Personally, I'm not a fan of book cases that are truly 'built in'. I would favor a free standing unit, even if it seems built in to the wall, which means I'd do the full floor first, but that is just my preference.

[Mark J]

Like others have said, full floor first and bookcase on top.  And I would design that book case to look built in, but to be removable.  Eventually either you or a future owner will want to remove the bookcase.  (Or maybe build a freestanding bookcase that you can take with you if you move).

[Jonathan McCully]

Thanks to all of the replies. I guess I should clarify. It's going to be cabinets with a bookcase stacked on top. Similar to the picture below.

I think I will install the flooring first after getting so many responses recommending that. Now to figure out how to glue hardwood to my concrete...

[Chet]

On 3/28/2025 at 6:51 AM, Jonathan McCully said:

Now to figure out how to glue hardwood to my concrete...

Look around, there are hardwood floors that still install like a floating floor.  

[Chestnut]

Are you dead set on true hardwood or would engineered hardwood be an option?

[Jonathan McCully]

5 hours ago, Chestnut said:

Are you dead set on true hardwood or would engineered hardwood be an option?

My preference would be hardwood. I’ve got engineered through most of my downstairs and it’s already gotten marred and gashed quite a bit in 3.5 years and I can’t do anything about repairing it. I’d really like to have something that I can sand and repair if needed periodically.

[curlyoak]

A long lasting floor is tile. I installed my kitchen cabinets to the concrete floor. It was easy to get the tile tight against the cabinets. Also there is a big overhang supporting the weight is 2 4x4 legs. The tile trapped the legs in place. On a wood floor I would need to anchor the 4x4 to the wood floor with some sort of an L bracket.

[Chestnut]

On 3/29/2025 at 11:47 AM, Jonathan McCully said:

I’ve got engineered through most of my downstairs and it’s already gotten marred and gashed quite a bit in 3.5 years and I can’t do anything about repairing it. I’d really like to have something that I can sand and repair if needed periodically.

Some engineered hardwoods are better than others. It's possible to get an engineered hardwood with a wood layer as thick as a 0.25". These typically will allow for 1-2 full sandings. As a hardwood floor lover I've considered this, the deal breaker on engineered products is getting them unfinished to allow me to finish in place. While possible it's extremely limiting on options. If you get creating with spot treatments you can probably spot fix the manufactures finish with a hard wax oil finish. It will at least lessen the look of the scratch though it won't remove it like sanding.

The reason I'm pointing this out is installing hardwood over concrete is typically a no-no. solid hardwood needs to expand and contract with moisture changes, installing on concrete is typically a glue situation which can lead to issues. Secondly concrete can create a moisture imbalance where there is far more moisture below the hardwood than above leading to issues. Make sure your doing your research.

 

[Jonathan McCully]

Some engineered hardwoods are better than others. It's possible to get an engineered hardwood with a wood layer as thick as a 0.25". These typically will allow for 1-2 full sandings. As a hardwood floor lover I've considered this, the deal breaker on engineered products is getting them unfinished to allow me to finish in place. While possible it's extremely limiting on options. If you get creating with spot treatments you can probably spot fix the manufactures finish with a hard wax oil finish. It will at least lessen the look of the scratch though it won't remove it like sanding.
The reason I'm pointing this out is installing hardwood over concrete is typically a no-no. solid hardwood needs to expand and contract with moisture changes, installing on concrete is typically a glue situation which can lead to issues. Secondly concrete can create a moisture imbalance where there is far more moisture below the hardwood than above leading to issues. Make sure your doing your research.
 

Thanks for the info @Chestnut I’m planning to chat with a few of the hardwood suppliers in my area before proceeding. With regards to the moisture, I live in the desert, so I’m hopeful that I might be okay, but again, will be inquiring of people who know more than I do. I do wonder about possibly laying a subfloor with moisture barrier and floating the hardwood on top of it. Sounds like it might be a decent option that will allow for adequate expansion.


Sent from my iPhone using Tapatalk

[curlyoak]

I live in wet Florida. Most houses are concrete floors. Here they use a moisture barrier of various types. One type is cheap vinyl flooring. or high grade seconds. Also the wood remains a significant distance away from the walls. Avoids buckling. A molding conceals the wall gap.