Plywood, how thick do i need?

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Old 01-18-05, 08:08 AM
deckers007
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Plywood, how thick do i need?

I am putting plywood onto a floor with joists set at 24", what thickness of plywood should i lay in order to get less spring in the finished floor.

Chris
 
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Old 01-18-05, 08:40 AM
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REally would've like to have seen them at 16"oc but you've got what you've got. Sistering them would not be a bad idea to help take some flex away depending on what the rooms purpose is going to be. 3/4" minimum plywood, lay down a bead of construction adhesive over the joist before placing the plywood then screw it into place, don't nail it since over time the floor will get some "spring" in it being 24"oc, the nails will start to work loose.

Our house was built in 80' and uses engineered floor trusses 16" oc with 3/4" CDX subfloor nailed. I like to call it the trampolene house since you can damn near bounce like a wrestling mat and it sqeaks everywhere since it was nailed. Spans are too long to sister anything to them from the basement for strength so we'll have to wait until basement remodel and add walls to support the long spans. When we got to install new carpet upstairs in the next few months I'll be screwing all the plywood on the joists before the new stuff gets laid with hopes to quite down the sqeekiness.
 
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Old 01-18-05, 08:50 AM
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Plywood for joists on 24" centers

Placing joists on 24" centers reduces the number of joists by about one third compared with 16 inch spacing. Increasing floor joist spacing must be carefully assessed in order to ensure that adequate floor stiffness is maintained. Floor sheathing thickness will also have to be upgraded to yield equivalent performance.Typically, this means using a 3/4 " thick subflooring instead of 5/8 inch subflooring. One must consider the total cost of the thicker plywood versus the savings on the joists.
 
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Old 01-18-05, 09:00 AM
deckers007
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I really wish that they where on 16" centers as well. the rest of the home is build with 16" but when they came to the garage ii jumped to 24, even though the loft above the garage is already framed in, it is such a good space, we would like to turn it into a small apartment for extra $, it is 20X23, small but enough.

Can i add a joist between each, making 12" or is that over kill, what would be the pros and cons of doing this??

Chris
 
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Old 01-18-05, 09:28 AM
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12" oc would not be overkill and would really stiffen the floor up and allow the use of 5/8" subfloor. Only real down side would be running HVAC depending on which way joints are laid out currently, other than that it's done quite often in new homes when doing tile/marble since the floor cannot flex without breaking the surface ontop of it or at least cracking it (or chance at crack/break)

If you can get them into place it would help alot. Not only that but in the garage you'll have to install 5/8" sheetrock and have it taped so it will help avoid cracking joints with activity overhead.
 
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Old 01-18-05, 08:36 PM
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deckers007,

I'd say that using the idea that IHI would be the best approach, depending on your current HVAC system. This would stiffen it up to avoid any bounce, or minimal bounce and still allow for placement of duct work and plumbing runs until you get to a point to make a soffit for the dropped down lines. I would have suggested staggered blocking but the "apartment" idea put a stop to that thought.

The other issue is since you mentioned this may be a "rental unit", the codes within your area may require 2 layers of 5/8" Type X gyp.board regardless if attached or not with a living quarters above. This means you really need adequte support for the drywall as well as contact the City to acquire a permit for such a purpose. If you don't and a fire or damage is done of whatever type, your homeowners insurance may not cover you. Just a thought.

Hope this helps!
 
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Old 01-19-05, 10:53 AM
deckers007
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Thanks for the information Doug, our municipality called me back this morning actually and informed me they would not issue me a permit due to zoning bylaws. It seems like we own the property, but do not get to decide what i want to do with it!! it is very frustrating. Now i have 500 sq ft of space that i do not know what to do with.

Any ideas to get around this??
 
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Old 01-19-05, 11:06 AM
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deckers007,

You're very welcome.

I'm sorry for the bad news that you received. I thought if you hadn't checked on the issues I mentioned, you would be investing allot of time and money into this and then be surprised that it is an issue that many have to contend with.

One way is to ask for a variance. Unfortuantely, this is not a guarantee that they would pass it and in most cases, you would have to submit drawings which would cost some money and pay a fee for the request. In your case, all your neighbors would be asked to provide any feedback to this venture, merely saying no or yes with or without comment to a form sent out by the City. There would be a scheduled review board meeting to review this and of course the majority vote rules.

Zoning laws are suppose to be for the good of the majority but in cases like this, you feel that you are being cheated on opportunities that could prove vital to your retirement days and as you say it is my house but are limited to what you can or cannot do. I encounter this all the time in my profession and I have mentioned it many times within the Forums with many not happy with my remarks. Trying to do this without consent as I said earlier would be another problem and I don't wish that on anyone.

Beyond what I mentioned above, I don't have any other suggestions.

Good Luck
 
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Old 01-21-05, 08:18 AM
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Many jurisdictions are amending their building codes to allow for Accessory Dwelling Units (ADU) or better known as a 'mother in law' apartment. Jurisdiction recognize that illegal ADU's are being constructed every day and have legalized in order to ensure they are built to appropriate safety standards. They also recognize that ADU's are an effective way to increase housing units in urban areas with minimal cost and impact. You might want to approach the City again and see if their are planing efforts underway that would allow for ADU's.
 
 

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