Pier and beam foundation - Will it support a large tank?

G

GraviT

Premium Member
[We're moving at the end of this month to a home with a pier and beam foundation. I'm a bit concerned about the subfloor holding up my 120g tank when I get around to setting it up, and was wondering if anybody else has a large(ish) tank on this type of foundation. If so, how large is the tank? (mine is 4'x2' ) . I would also like to know who of those with pier and beam made an effort to "shore" or reinforce the subfloor for additional support, and what you did/used to do so.

The house we're in now also has pier and beam, but my current tank is only a 55g and has never been a cause for much concern. I just don't want to wake up one morning and find the top of my tank at knee level! :bomb:]



Edited By GraviT on 1115185850
 
[Kevin I am attaching a link that can help you with the weight of the tank and all the things inside. Maybe that can help you determine how much extra bracing you need underneath the house. All you need to do to help support the tank is to get some concrete cinder blocks, one 18" square concrete pad, a piece of sheet metal and some shims made from a 2x4, What you will do is place the pad centered under the floor joist that will be directly beneath your tank. Then stack the cinder blocks on the concrete pad. You are trying to get the gap between the floor joist and the cinder block to approximately 1". Place the sheet metal on top of the cinder block forming an upside down bowl. You will then take 2 2x4 shims coming towards each other and wedge them together between the floor joist and the cinder block using a hammer to secure firmly. One word of caution here, you are not trying to raise the floor so your task is to make it tight. Once you have your tank filled you will need to check your floor for level. Because of the shims you can raise or lower that portion of the floor. You can do this under the tank in other locations to firm up the entire area under the tank. I have also used multiple piers and ran 2x6's or 2x8's between them and leveled and supported larger areas as well. By the way the sheet metal is used for an insect barrier. For some reasons termites do not like to go upside down and around the bowl effect.

Steve

Tank Calculators]



Edited By Bustedup211 on 1115186601
 
[Thanks for the tips Steve, I am a bit confused though (not entirely an uncommon thing). You mention that the sheet metal should go on top of the cinder blocks and form an upside down bowl, yet you also say that the shims go between the cinder blocks and the floor joist. Could you clarify this part a bit, or perhaps have a picture of this setup? I'm not sure how to form the bowl from the sheet metal, and the shim thing has me totally lost. ???

Thanks again!]
 
[The shims go on top of the sheet metal. The sheet metal would be placed on top of the cinder block and then bent towards the ground to form what might look like an upside down bowl. I hope that explains that a bit better. I have a fuzzy brain sometimes because of pain meds I take so I do not doubt that I could confuse someone....hehehehe lol los?]
 
[One more thing about the sheet metal. Make sure that you have at least 3 inches of metal beyond the edge of the cinder block and that the edge has a couple inches of clearance from the cinder block. clear as mud huh]
 
[I was a real estate broker for 6 years and did house rehabs so that is where I received my training. FHA would say that you need to use mortar to adhear the blocks together but it really would not be necessary for your purpose. The only time that this might be an issue is if you refinanced using FHA financing and the appraiser looked under the house and happened to see the pier(s). Not likely but just an fyi. Conventional financing only concerns themselves with a clear termite inspection and the way that this is built would provide just that.]
 
[Kevin,

I never thought of the cinder block solution but I do have a peir and beam house and did reinforce my floor. Like Steve mentioned the goal is not to raise the floor but simply reinforce it.

First, determine where the tank is going to go and see what is under the house in that location. In my case, I had a pier in the back left corner of the tank, I had a pier running parellel to the back of the tank and had floor joists running perpendicular to the tank. I created a header out of 2 2"x6"x5' nailed together and secured them in place with jacks. I installed the header parallel to the tank in front and added a support jack to the beam in back of the tank.

Here is how it is installed from the ground up.
1. dig out a bit of the dirt and insert sand into hole (goal here is to creat a level starting point)
2. Ideally pour a concerete pad with reinforcing rods. In my case, I used a couple of premade cement pads.
3. Then comes the adjustable steel lally column (I found these at Lowe's). They use these around here for setting up mobile homes.
4. Then the header is placed on top two of these setups and raised snuggly into place against the floor joists .

Here is a visual idea of what I did on my house. The side view depicts what I said above and the top view is a birds I view of how things are sitting.

foundation.jpg
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You are more than welcome to come crawl under the house and take a look.]
 
[Kevin,

I'm a Project Designer for a Structural Engineering firm here in Dallas, and have my BSAE in Architectural Engineering (can't say I'm an Engineer yet because I'm not taking the license exam for another year).

Steve has a good idea as far as the termite shield is concerned (also what it does for you is allow you to see a termite tunnel, should they try to gain access to your home there).

Todd's idea is a bit more elegant, and could work.

What both mentioned, but failed to point out is that you do need to be concerned with "raising" the floor by uplift of the lovely expansive clays we have here in Texas (especially over in the Los Colinas area). Depending on what type soils you have under your home, the site drainage, and ventilation of your crawl space, this may or may not be a problem for you.

I'm assuming that the house you're purchasing is older, since most modern tract builders use a post-tensioned slab on grade. If it IS a newer house, then that foundation system is suggestive of expansive soils.

The additional support you're thinking of may, or may not be needed depending on the structure directly under the area you'll set the tank on.

Once you've moved in and decided on a location for the tank, I'll be able to help more...(you could take pictures, or I could take a look at it for you).

If you have more questions, feel free to ask.

Geoff]
 
[Good stuff! Thanks guys! Only other question would be how in the heck do you figure out exactly where the heck you are under the house? My current house is pier and beam also, and I ran wires for the surround sound system in the living room (something else I have to do while I'm down there). It's dark, dusty and confusing under there!]
 
[Kevin,

When I am under the house I tend to look for land marks. I look for them in the house first, then in the crawl space or attic.

For example, I can see the plumbing for showers and toilets, power to outlets and return ducts for the heater/AC. Otherwise, I have to estimate how far from the entrance of the crawl space something is and then work from there. Luckily my house is relatively small and I can find everything pretty easy.

Geoff,

How to you take into account the expanding soil under the pier and beam house?

I have not noticed the cracks in the soil under my house changing much over the years I have been under there. I have by no means done a scientific study, but on general appearance it seems stable.]



Edited By patteto on 1115216705
 
[One thing to recommend for yourself and anyone who crawls under houses.

Invest $9 and buy yourself a non-contact voltage sensor at Lowes or Home Depot. They will be in the electrical section, and are commonly referred to as hot sticks.

When under a house, always check any ducts or piping (anything that could act as a conductor) to ensure they are not hot before touching. The last thing you want to do is act as the ground! :shocked:

You never know when you will grab hold of something while trying to brace yourself before you realize what your doing.]
 
[Todd,

Without getting into a LONG (and probably amazingly boring to most people) discussion, a pier and beam foundation is designed to support the house ABOVE the soil. (Imagine digging out a 6 foot hole under your house - it would then be supported on the "stilts" of the piers and the "beams" of the grade beams).

Since the clay soils that we have here in Texas like to change volume (expand/contract) when there is a moisture change IN THE CLAY, these pier and beam foundations are designed so that the grade beams are actually NOT sitting on the soil. This little space below the grade beam gives the soil room to expand and contract without having an effect on your house.

The amazing thing about the soil here in Texas - it varies. For example, I live in the Centerville-Broadway area of south Garland - close to Duck Creek. My house is on AMAZING soil...almost no clay at all ( I know because I had to dig 9 feet into my back yard to fix a plumbing pipe). The street behind my house (closer to Duck Creek) is on a HIGHLY expansive clay - you see all sorts of damage to the houses (also they are newer, and most likely not pier and beam, but slab on grade).

All this being said, it's entirely possible that your house sits on a good soil with little clay, and therefore you've had no problem. Another possibility is that your site is graded properly, and you don't have moisture variations in the soil under your house (which is how it SHOULD be).

If you were on an active, expansive clay, it's possible that your shoring could be "lifted up" by the clay when it expanded, making your floor "rise", or even damaging the structure.

If you were on an active expansive clay, there are other ways to reinforce the structure to support the additional weight (that's where a Structural Engineer comes in). Even using your idea on an active clay would work, except instead of leveling sand and a concrete pad, you'd have to add a pier that would be able to support the load you're putting on it, and also be able to resist the uplift caused by the active soil. Obviously adding piers under a house that's already built is VERY expensive, and don't EVEN get me started about those so-called "foundation repair" companies :very angry:

Guess I blew the idea of not being long and boring straight out of the water...lol. I hope this answers your question. If not, let me know - obviously I like to ramble on about the topic.]
 
[Geofrey I must say you have to love an engineer. The purpose of the shims that are installed is two fold. First it is easy to adjust up. Second it is easy to adjust down. If this is an older home the soil moisture content should be easy to see once under the home. It is is high then Geofrey would be correct that you might have issues with movement. If this is the case the next best recommendation that I would say would be to take two laminated 4x4 beams that are 2x as long as your tank if possible and run them perpendicular to the floor joist. Use a couple of bottle jacks to firmly snug them in place, Prior to putting the beams in place take 1/4" angle iron and bolt it to each floor joist using 3 bolts per plate. the angle iron needs to 8" in length. Then take u-bolts from under the beam and insert them into holes that you have drilled into the angle iron and secure with washer and nuts. You can lay out the angle iron and beam and u-bolts prior to taking under the house so that your holes will line up. The good thing about this setup is that it does not contact the ground. The way it gives strength is by moving the load to a larger area of floor joist and should move it towards additional piers thar are already under your house. We have used this method for strengthening for water beds so it would work as well.

steve]
 
[Geoff,

Your explanation was great. I think I understand most of it.

The only comment I will make about the new slab houses versus pier and beam houses is that I think my 50 year old (live by White Rock Lake) house seems be built much better than the "new house" (generic north Dallas house) I owned in Flower Mound.]
 
[Todd, glad to be of help! I also prefer older houses, working in this business, I see a lot of stuff in new home construction that really irritates me...(and this coming from an engineer) ... lol. I've designed a few $$$$$ homes for the Dallas area that were all pier and beam. IMHO, it's just the best system for this area.

Steve, I'm not sure if I read your post correctly, and I don't intend on starting a flame war, but your facts are way off.

Shimming something up is very easy, removing shims from between two pieces of wood that are being clamped together with 100 to 900 pounds PER SQUARE INCH is not easy, if even possible.

Seasonal moisture changes in clays can be at the surface, and easily identified, but most likely they are deeper than that. I've seen sites where the clay 10 feet subgrade has caused 3 1/2 inches of uplift.

In GENERAL, in the Dallas area, the largest soil concern with most foundations isn't shrinkage, but expansion of clays and the uplift caused by that expansion.

If your idea of the 4x4 is to hang one from the joists, it's simply a bad idea. Wood is awful in tension (ie - hanging the 4x4 from the floor joists - ESPECIALLY putting bolts in the tension fibers). Wood (when designed properly) is used in it's strongest properties, bending and compression. Connections should always be in bearing. Your suggestion relies on deflection of the primary members before ANY load is transferred to adjacent joists, and depends on a tension connection to transfer load.

Sorry to rant so, it's just that I've been in the construction industry for over 15 years, and I've seen too many "I always do it this way" solutions that may work for a while, but are really accidents waiting to happen. Most people that rely on this and "I've never had a problem doing it this way" aren't around long enough to see the problems that arise. This is especially true in wood frame construction, where the material is not man-made, and doesn't have consistent properties. Homebuilders have a one-year warranty. Structural Engineers have a TEN-year limit of liability per the law...but are morally responsible for life.

That is a big part of the reason I offer my assistance. It's always better to be a little conservative and RIGHT when you're talking about structure...something that is VERY expensive to fix, and VERY dangerous if done wrong. One acronym that I've heard many times over the years explains a lot about construction. "KISS" - Keep It Simple, Stupid.


It is entirely possible that he won't need to do anything to set a large tank, and it's most likely that any correct solution will be fairly straightforward. The number of solutions (member reinforcement, load distribution, load transfer) are only limited by the designers creativity. The number of PRACTICAL solutions is limited by time, space, and budget.

People can say, "I've done this" or "I've done that", but the correct solution for Kevin can only come after the UNIQUE situation he has is looked at.

Whew, again....I don't mean to personally attack anyone, but I deal with this stuff for a living, I've seen the issues as a home owner, construction worker, contractor, and Engineer, and I may be a little short (albeit long winded) when I see something that's given as fact, and in fact is not true.]
 
[Geoffrey I agree with you and I also am not trying to start a war. My suggestion with the shims can be changed by using a screw jack between the floor joist and the cinder block. I came over from Louisiana where it is not uncommon to see a 5 to 6 difference in the level of a house due to red clay. I think we both are suggesting things that work and what will be needed is a look at the property.

The idea of the 4x4 lam beam comes from bridge construction. The effect is to transfer the load to the anchors or pilings of the bridge. This would be the piers on the house. I agree that this would not be as good as using piers but in an area that has lots of soil movement the house would be showing this now with cracks in walls, gaps in window casing, doors that do not close or actually go through the door frame. I have seen all of those things. While I did not finish my degree in constuction engineering (this was over 20 years ago so I must admit I probably have forgotten the exact formulas wihich is a problem in this case) but I was involved in the building of houses for 8 years.

I am not an engineer but I have to say that what I have seen and done that has worked should be considered in this matter. My ideas have been simple and easy to accomplish and would give the opportunity to be adjusted when needed. Ok so I am hurt a bit here. I have built and designed things that have and have not work. What I have proposed I have seen work and work for YEARS. That is all I have to say.

Hopefully Geoffrey we can agree to disagree and still be friends. I enjoy a good debate.

Steve]
 
[Steve,

I think agreeing to disagree is fine...
as long as I'm always right :rasp:


Seriously, didn't intend to offend or insult you personally, and I also love a good debate (when I know what I'm debating about..someone tell my wife that...LOL)

It's frustrating that people wouldn't have their neighbor perform open-heart-surgery, or act as their lawyer, but yet will take as fact the neighbors opinion about the structure of their home...which could be a life-threatening mistake about something that is their biggest financial investment.

Part of the problem is that people just don't have the facts about materials, properties of materails, and don't understand statics and dynamics, or worse, they think they know, and they have the facts wrong. I don't understand the first thing about neurological function in the frontal lobe, just like most people, but I do know about structural engineering, unlike most people.

With the start of the do-it-yourself-home-improvement craze, people realized how easy and simple it is to paint, hang drywall, change a light switch, or replace a faucet. Unfortunately they think it's also that simple to do structural modifications.

The misconception is that engineers design bridges and skyscrapers, and everything else can be done like it always has. In fact, I bet I could walk up to ANY non-engineered structure (and some engineered) and point out at least 4 things that are either against the code (and therefore the against the law), or just plain wrong.

I guess part of my anal-retentiveness about "do it right, or don't bother" comes from (don't tell anyone...I'm so embarrassed) being born and raised in Michigan. I got to Texas at age 18, and have been here pretty much since then.

Anyways, my offer to help Kevin, or any other member of this board stands.

Geoff]
 
[I was kidding about being hurt. My point is that difference of opinion is what made a Ford a Ford and a Chevy a Chevy. Engineering was different but both worked. One would say better than the other depending on where it is you worked.
Same thing here. Your opinion is based on your experience and knowledge where another engineer might recommend something totally different but still within code (which is another matter all together). Will one work better than the other maybe maybe not. Will both work equally well.....same goes. I have to say this I have been around long enough to have seen engineered projects that would not work and had to be changed by a carpenter who has been doing that work for more years than could be counted. Education is just that whether learned through college or through the practical application of sound building strategies. I like you like a good debate and agree to disagree so long as I am right.... :rasp: back at you lol lol]
 
[Hehe, you guys crack me up! :lol:

I went back out to the house today, but didn't get a chance to crawl under the floor yet. One thing I didn't think about before is the wall behind the tank sits on the concrete foundation (the other side of the wall is the garage, the floor of which is at ground level).

In theory, the back of the tank should be inches from the header and joists, both of which would be resting on the concrete foundation in bearing. The setup will sit perpendicular to the floor joists, which is ideal for this situation.

The big questions are: What size are the joists? How long is the span? How far apart are they? I should know in a couple of days when I finally decide to crawl under there and take a look. Of course, the access hatch is all the way on the other side of the darned house.]
 
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