We are about to begin an addition project on a pier and beam built home. After meeting with out builder we discovered that the engineering plans appear to be several inches off which, of course, affects several different aspects of the foundation. The project is pretty straight foward so I think I can explain the potential problems. Our existing home has a concrete beam around the entire perimeter with a double row of bricks about 12-14″ high that the home sits on. The crawl space is quite decent since the original grade is about 6-8″ inches lower than our existing yard. As for the addition, the engineer has drawn plans that mirror the original home but seems to have miscalculated the distance from the current grade to the new subfloor. After field measurements with my builder we discovered we will have about 28″+/- of space between the grade and subfloor. The engineering plans call for a concrete beam and the double row of bricks with 2 x 10 joists. This puts us very close to 18″ of crawl space. The engineer has called just for regular wood. Our codes indicate that we must use pressure tretaed wood if the crawl space is less than 18″. To us, this is too close to gamble with and we think we should use the pressure treated wood. My builder also has some opinions. First, he thinks using bricks to support the house is not strong enough and would prefer us to pour a concreate beam with brick ledge that went up as high as the sill plate. Second, he would prefer to use 2 x 12 joists instead of the 2 x 10 called for in the plan which would obviously drop it to below 18″. Any comments or suggections would be appreciated.
All of the above led to some other concerns regarding the foundation. The engineering plan calls for piers to be set in the interior of the crawl space to support a double 2 x 12 beam that the floor joists will intersect with. He calls for galvanized joist hangers to hold the floor joists. My builder is concerned that over time the pressure treated wood will corode the joist hangers. He thinks we should either put the beam lower so the joists run over the top–the span only ranges from 17-20 feet. He feels this is short enough to run solid joists all the way across with the beam underneath in the middle for support. The only problem with this idea is that the beam will be almost touching the ground which does not seem like a good idea. The second suggestion is to pour the support beam in concrete equal in height to the perimter beam without the piers. To me, the lay person, this seems like the best idea. The only disadvantage is that the crawl space will be divided and air flow could be compromised. We would put crawl/vent spaces in the beam but I do not know if this is enough to keep the air ciculating and the moisture out. Once again, any comments or suggections would be appreciated.
Thank you for your help.
John
Replies
How about just excavating to get a deeper crawl space and avoid the pt issue?
Your builder has two good ideas - beam below joists and concrete vs. brick to build up the footer (assuming you really mean brick and not concrete block).
We were worried that digging below the grade of the existing yard could possibly lead to water draining and getting trapped under the house. The plans were for two rows of regular old brick.
Thanks
Your post brings up several points.
I'd be rather inclined to know what supporting evidenece the engineer has to support his design. Further, by what process he sized and specified framing that might be too close to a soil-floored crawlspace.
My experience is that few permit offices or BIs will permit a clear (bottom of framing) to soild distance of less than 24". Most want to have some form of access from the existing foundation space to the new, too--if only to permit termite inspections/treatments.
My local AHJ would not permit framing closer than 24" even if PT (even over a "rat slab").
So, I'd be back to my engineer with some pointy (if polite) questions. I'd start with the big-ol' beam--Mr Engineer, will the AHJ make us add a separate crawlspace access? I'd start by making it at least sound like you and engineer versus BI/Permit office. That allows the engineer to maybe think about any uh-ohs without being in 100% defensive mode.
If that doesn't work, see if the drawings will pass permits. If they don't, Mr Engineer (likely) has a duty to bring them into compliance with local codes. This is what you paid him for. If you didn't pay him, somebody did--and that person is owed compliant drawings and materials.
But, that's just my opinion, other may differ.
"Once again, any comments or suggections would be appreciated. "
The obvious thing is to talk to the engineer. That said. 18" crawl spaces are okay here. (NY) Galv. joist hangers aren't a problem if you aren't using pressure treated wood, otherwise I'd spring for stainless steel. You should probably talk to your bldg dept about code issues.
I would consult an architect, your engineer may not be up on the codes .Architects design houses, engineers do work specific to the type of constuction, structural, electrical etc engineers.
mike