Raising family room floor

[JimAlsup]

Hello All,

 

We're doing a addition/remodel and I need to determine the best way to raise an existing step down family room.  Attached off this room will be an addition with crawl space.  The attached image shows the design I have using sleepers and joists.  This design seals off the sub-floor area from air circulation making it a dead space.  Alternatively, I could reverse the direction of the sleepers/joists opening up this small space to air circulation from the attached crawl space.  I've look through the foundation sections of the ca 2016 building code but came up empty.  Anyone understand if there is a code issue here and if not what the best approach is?

 

Thank you,

Jim

[Doug_N]

A floor plan would be a good thing to see, and perhaps the plan file.  You can attach files by clicking on the "choose files..." link at the bottom left corner when you are composing a message in this forum.  

 

Also please take the time to fill out your signature

[ACADuser]

And what climate are you in?

 

[Kbird1]

More information is need really especially if you want Code help ...ie where are you?.....but some general advice......

 

1.) there should be VB under the existing Slab........putting it on top too will cause it to "sweat" in my experience ( if moist is present in slab....should be tested).

2.) All Sleepers should be on sill gasket not VB.

3.) 2x8 joist will be "bouncy" if Span is more that 8'

4.) Use a Ledger to double up at edge of existing slab (over Sill Gasket if touching concrete) for better nailing of J.Hangers and Flooring

              ( don't allow Sheet joins at this point, lap new ply 2' either side (Or more depending on direction)

5.) excavated Soil needs to be covered and sealed with VB AND preferable a 2" thick "Rat" Slab of concrete to retard Moisture and vermin.

 

M.

 

Please do your Signature, thx !

[JimAlsup]

Hello All,

 

Thank you for your replies.  I've answered some questions and asked more based on peoples comments.

 

- Signature Done. 

- Climate here is great, just a tad, ok more than a tad, smokey these day.  Rainfall is 19" a year. Zone 3 according to this: https://www.norbord.com/na/blog/whats-your-building-science-climate-zone/

Regarding Comments from TBIRD1:

- #2 I don't know if a VB exists under this 1955 slab. If code required it back then, then I'm sure there is one.  There is an existing VB (lining) under the carpet, but that was just something the carpet installer did/suggested.  I've never seen any moisture issues, but I will test it at some point, but it sounds like your saying it would be a bad idea.  What I really need is a pointer to the code on this kind of retrofit as I couldn't find any myself.

- #3 Tables says it's ok to span 12' for 2x8 joists with 16" O.C. Would blocking or bridging at 6' eliminate the bounce?

- #4 Yes, I didn't show any ledger on this foundation drawing.   The current wall at the edge of this foundation will be gone, so I could change the blocking 2x4.75 over the existing sill into 2 2x4.75 ledgers. This would still give me a way to run the floor structure and have an air opening to the crawl space. 

- #5 The city told me In our area there is no crawl space VB required unless the interior ground to stem wall top is less than 18".

 

I have attached a pic of my addition foundation outline showing the concrete slab in question. The foundation setup in very incomplete.

 

Thank you,

-Jim

 

[Kbird1]

Building Codes are different everywhere , even City to City boundary , so they ( City Official) are your best Guide, though admittedly some are not that helpful , as if you are "Designing it, you Should know" , at least that is how some Officials think.

 

It is quite possible in 1955 no VB was used , codes were very lacks back then and very tough now especially in Cali., Perhaps your Carpet Installer "knew" something?

 

You maybe be Best to contact one of the California Based Designers on the Forum like Richard Morrison (in PaloAlto?) or Perry (Drawzilla).

 

My comments were based on personal experience as a Design-Builder , not necessarily "Code" , as when I posted I didn't know where you were located.

 

The American Wood Council has Span Tables for Free (PDF) and an online calculator and also free Android and iOS Apps, along with other Design Papers etc available for all to use. Not sure about your local City but my mine has Handouts for Home Owners for common things like Garages Basements etc.

 

Calc.

https://www.awc.org/codes-standards/calculators-software/spancalc

PDFs

https://www.awc.org/codes-standards/spantables

 

 

[DRAWZILLA]

I deal with 50 different cities here in southern Calif. and most cities have their own way of applying the codes, it's best to check with the city or county the work is in, I check with each city to be sure.. The most change in in the zoning and municipal codes, you can check all that online.

[JimAlsup]

Hello All, 

I've been to the city building/planning dept a few times for questions.  You sign in, wait for your name to come up and then they may or may not be able to answer a question.  Time consuming and frustrating. A couple of inspectors gave me their email addresses, but so far they just ignore my questions.  I feel like there work time is pretty booked and the only way to get cycles where they will actually help look things up is to travel, sign in, and wait.

 

I think the kind of questions I have this project should be answerable by a local structural engineer.  And I will need one for plan checks/signoffs anyhow.  Any thoughts on the best way to find one?

 

Thank you,
Jim

 

[DRAWZILLA]

15 hours ago, JimAlsup said:

Hello All, 

I've been to the city building/planning dept a few times for questions.  You sign in, wait for your name to come up and then they may or may not be able to answer a question.  Time consuming and frustrating. A couple of inspectors gave me their email addresses, but so far they just ignore my questions.  I feel like there work time is pretty booked and the only way to get cycles where they will actually help look things up is to travel, sign in, and wait.

 

I think the kind of questions I have this project should be answerable by a local structural engineer.  And I will need one for plan checks/signoffs anyhow.  Any thoughts on the best way to find one?

 

Thank you,
Jim

 

I guess the best thing would be to submit a plan for plan check, only then will they give you the time to go over all the things you might want to know. As for an engineer, find one and if he or shy is not what you want then try another one you can work with. I have been working with mine for over 30 years now. 

[JimAlsup]

I discussed this with the city today and got a guy who was more responsive.  He didn't consult any code docs, but thought I could run sleepers either way and that opening the area to the new crawl space would have advantages.  He said no vapor barrier was required under the floor when it was built in '55 and as it's an existing living space, a vapor barrier is not required under the new floor, but suggested it was a good idea.  He also suggested batten/net floor insulation at installation time as doing it later would be  difficult.

 

So I think I'll go with this approach. Thank you for all your help.

-Jim

[Gawdzira]

If the concrete is raw, I would paint it with Xypex to help with any future moisture issues.

https://www.xypex.com/

 

For insulation, I would use closed cell rigid foam sheets cut between the sleepers. 1.5" would be plenty as it sounds like they are not requiring r-19. I don't like your ledger detail. I would put something more stout on where you are nailing hangers. Probably 1.75" x 11.25" LVL rim joist that gets some nails into the sleepers and bolted to the concrete. (that is how I would present a sketch to an engineer and then ask him/her is this will work?) Isolate is from the concrete with Bituthane. Absolutely put down a vapor barrier at the new crawl space. I would use 20mil plastic (Stego Wrap) fully taped at seams and running up the walls and taped to the walls.

[Kbird1]

All Good by Alan above , this is similar to what I posted earlier.....

 

Do not use the white styrene between the Sleepers , it is next to useless as far a R-Value use one of the Dow Products , locally it is blue or pink depending on r-Value etc.

 

I have used Laticrete HydroBan on existing Floors before to retard moisture if the concrete slab is old cracked or may have moist issues etc . Roll the floor twice , once in each direction with a 19mm Roller Sleeve and disposable tray etc. it sets up as a thin layer of rubber like Membrane. We also use it to waterproof out Tile Showers, so any left overs won't go to waste if you have two bathrooms to do too.

 

If by batten/net insulation between the joists in the new area, you mean you intend to use fiberglass batts, I'd be inclined to use Rigid there too, sealed in with cans of spray-foam, especially if you intend to heat the floor eg under Tile in the Bathrooms. You could also do a Foam sandwich with 1/2 ply on the Joists. 2" Dow Foam , then 3/4 ply on top..... this means hanging ht joist 2.5" lower though and perhaps double bottom plates , but has worked well in the past for me.

 

M.

 

[JimAlsup]

5 hours ago, Gawdzira said:

If the concrete is raw, I would paint it with Xypex to help with any future moisture issues.

https://www.xypex.com/

 

For insulation, I would use closed cell rigid foam sheets cut between the sleepers. 1.5" would be plenty as it sounds like they are not requiring r-19. I don't like your ledger detail. I would put something more stout on where you are nailing hangers. Probably 1.75" x 11.25" LVL rim joist that gets some nails into the sleepers and bolted to the concrete. (that is how I would present a sketch to an engineer and then ask him/her is this will work?) Isolate is from the concrete with Bituthane. Absolutely put down a vapor barrier at the new crawl space. I would use 20mil plastic (Stego Wrap) fully taped at seams and running up the walls and taped to the walls.

 

Thanks for the tip on Xypex, I will do this or something similar.  No floor insulation is required for this case, but I certainly will do something (probably the same

as I do for the addition floor). I have plans available to me for a number of homes in this 40 home tract home I haven't seen any plans for these homes adding a vapor barrier for the new foundation crawl space.  It's not required unless the stem wall is lower than 18".  I've also never observed any moisture intrusion in the existing crawl space despite the homes cap cod design (no roof overhang). I don't imagine the costs is high, but I'm not sure about the value. Subterranean termites would be deterred by such a vapor barrier?

 

In this situation I cannot use a rim joist > 7 1/4 inches and any such rim joist would block the airflow. I'm leaning towards reversing the direction of the sleepers to open the space to the crawl space air circulation.  In this case I will rest the new foundations 4x8 girder/joists directly on the sill and join perpendicular 2x8 joists to it.  This will be no wall over this foundation so floor nailing will not be an issue.  I'll try to post an updated foundation pic once I find time to do it.

 

Thank you for you help,

Jim

 

[JimAlsup]

Mick,

 

Thanks for the tips.

 

Jim

 

[Richard_Morrison]

Presumably, this is a crawlspace addition in front of the existing garage slab. I would be VERY surprised to see an existing 28" deep existing garage footing for a 1955 slab in this geographic area. You will likely need to reinforce the existing footing where it gets undermined by the new crawlspace excavation. Also, keep in mind that if a garage slab, there is probably a slope to it, so floor joists will need to be ripped. This could mean a difference of an inch or two in the lumber size. Your anchor bolt  design will likely either split the mudsill or spall the concrete. There are better systems for this situation; see the Simpson Strong-Tie catalog. I don't now how much addition you're talking about, but by the time you get done with all of the excavation and underpinning, and worrying about crawlspace venting and access, you may be be better off just extending the slab.

[GeneDavis]

Cannot comment on code, but . . . 

 

The carpenters that put down that subfloor work atop the existing slab are going to need some beers after all the work they'll do to get the top surface of the ripped joists good and level.  Unless that slab was poured to WalMart flatness specs (and has stayed that way for 63 years) they will do a lot of work to make things good.

 

I would lean toward specifying a minimum 1/4" space between the resawn joists and the sleepers they bear upon.  The crew can prepare some ripped 2x stock at various thicknesses to use when laying the joists in place.  Toenailed spikes can go through all.

 

As for good building practice, I'd specify pressure-treated materials for everything:  joists, sleepers, and even plywood subfloor, and hot dipped galvanized fasteners.