NEW CONSTRUCTION, Slab on grade VS conventional crawlspace

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I'm currently working on converting my first single family rental into a duplex in Washington State. I will be keeping this project in my portfolio for years to come. I'm trying to figure out best practices from more experienced investors and builder for constructing a high quality and low maintenance rental, so no better place to start then with the foundation.

My question is,
If you could build a portfolio of multifamily rental properties to hold for long term, would you build a slab on grade concrete floor (no crawl space) or standard conventional wood framed floor (has a crawl space)

There are pros and cons to both but just hoping to get some people who might have other insight on it.

Appreciate any and all feedback!

Newbie from Washington State

Here in Connecticut resale value of a slab homes is terrible.  No matter which foundation up here you need to go down about 4 feet to get below the frost line.  So why not go an additional 4 and have a full basement?  That way they have storage and a place for the washer dryer without the expense of a laundry room.

Here in my area of Maryland I would go with a full basement , with poured concrete walls . Its much easier to do plumbing and duct work in a basement than a crawl space .  Plus its great for laundry , water heater , and furnace location . Cost wise on new construction is only about 10 grand more 

Dominic thanks for the thought on resale. I will check with my agent and see what data they can find on resale for slab on grade vs conventional. Matthew I really like the idea of putting all the mechanicals in the basement. In the area of Washington I live in the frost line is only 18 inches. We are basically at sea level. Also the water table in this area is to high to build a full basement with out fully fighting water every step of the way.

I was kind of leaning towards slab on grade for a couple reason.

1. Lower constructions cost
2. Quicker construction time.
3. Possibility to have level entry into home for wheelchair access.
4. Durability of concrete floors with a vinyl tile flooring over the top seems very bomb proof from tenants and water.
5. No crawl space for rodents and other things to call home.

Thanks for the feedback!

Go with a crawlspace and then grade the property so that you still have an entry without a step up. With the water issues in your state you want a good grade flowing away from the house anyway to keep moisture at bay. 

@Tristan Brenner. I practice architecture in CT. The first thing you should do is become familiar with the current building codes in your state. Most states are now using some modified version of the IRC (International Residential Code). Requirements such as footing depth, concrete reinforcement, insulation requirements can vary from state to state, but all of those components will affect your construction budget, especially if you are constructing multiple units. Sounds like you need the help of a good architect!!!

@Elizabeth Zieman Thanks for the thoughts on the building code modification. I just recently finished up a custom home build and have found a great architect and engineer. I will definitely consult them before deciding which way I will go. Have you designed any houses that have been slab on grade? If so have you came across any thing else to watch out for? If I did radiant heated concrete floors with a smooth sealed finish. Would It be weird if I didn’t put any additional floor coverings over the finished concrete? Seems like it would be warm, durable, long lasting and cheap. Thanks again for the input! 

The answer to this question is dependent on a fair amount of factors: cost, performance, maintenance, soils, drainage, fill requirements, location, ect. ect. Both options have their pros and cons but I would focus on what is typically done in the area you are investing in. Here in Florida the difference could add up to thousands in one way or the other but it varies from lot to lot.  

Answers here are all good - I'll throw in a California perspective which may apply.  We have seismic considerations on all of our construction, and any chance of liquefaction generally means post-tensioned slab.

Not sure what WA is doing for seismic these days but I know the Cascadia subduction zone is getting more and more attention.  That could trigger future building code requirements that could impact resale down the road.

Take with a grain of salt, I'm not a soils or foundation engineer but just adding some observations.

I think the climate should be taken into account. Here in Nashville we are using slabs on grade, but it doesn't get too cold here. The radiant heating is also a great idea in a colder climate. I saw you mentioned putting tile floor over the concrete. Why don't you just polish and seal it? It looks great and will hold up great against large dogs.

Another thing to consider. You may need to use a truss system to run the ductwork in the ceiling. Another cool idea is to leave the ceiling open, paint the joists black, and shell out for some nice modern exposed ductwork. This looks really good with the concrete floors.

@Roberto Gutierrez The climate here is fairly mild. There are some large developments in my area that are all slab on grade homes. I will defiantly be doing radiant heat, it seems cost effective, low maintenance and comfortable.

In an above post I did say that I was going to put vinyl tile down but I do plan on polishing the concrete and have that be the finished floor. I should of specified that I was only thinking in the bath rooms for more traction when getting out of the shower because concrete can be slippery. The more I think about it people use rugs to stand on when getting out of the shower.

Thanks for the input