Gotta Love The Permit Office

DecksEtc

So, I finally got the permit back from the building dept. for the large deck project I've mentioned previously. They're "red pen" edits were absolutely classic.

It is a two level deck but the lower deck is what they somehow thought it was necessary to change. The lower deck is 16' x 22' and is only 4' above grade. I have 3 triple 2"x10" beams with footings spaced 9 1/2' apart - so three sets of 12" dia. footings.

Here's the "changes" to the drawing I get from the builing dept.:

They changed all of the footings to 10" dia. footings and wrote in that the center footing had to have a 14" dia. base

The reason behind only the center footing to have a 14" dia. base completely baffles me. Also, I have no idea why they would change the footing size to smaller ones. Those that know me, know that I always overbuild - I also detailed the larger footings in the quote

Also, my details list on the drawing specified that I was using triple 2"x10" beams for the lower deck yet they felt compelled to to mark up the drawing with red pen and repeat the fact the beams were to be triple 2"x 10"'s

I swear that if they don't use up their quota of red pen they aren't allowed to issue a permit...

Rant over, thanks for listening

Windwash

Your footings on the outside of your deck are carrying less weight than the center footings, that is why they are different sizes.
We usually bell out the bottom 12" of these center footings to the size desired and use a 12" sonotube for the top 3/4 of the footing

DecksEtc

I don't think you got my explanation. I have 3 rows of three footings in each row. I have 12" dia. sonotube footings for 6"x6" posts for a deck that is only 4' above grade. They only specified ONE footing - the center one in the middle row, be belled out to 14" dia.

There is no logic to their "red pen" changes.

BTW, I didn't question it, I just did what they asked for.

naptown CR

This is absolutley correct!

Think about your area of influence on each post. Sketch up your deck with the three rows of beams and footings. I assume that the two outer beams are on the edges of the deck. Now divide the space between each beam in half If you take the three areas you will notice that the center beam carries 1/2 of the weight of the deck. ( this beam is carrying the weight from 1/2 the span of the joists on either side).Now the beam in the center is carrying 1/2 the weight of the deck this post is carrying the weight from 1/2 the span of the beams from each side. Even though there are 9 posts 25% of the deck is sitting on the center post. For this example I have assumed that all other posts are at the perimeter and not set in with cantilevered joists but the principle is the same. I would have made the outside posts of the center row 16" and the middle one 24"


By the way what is the assumed soil bearing there?
No matter what I use 2000psf which is about as bad as it gets

greg24k

In NJ you cannot have a 12" footing for a 6X6 post, it has to be a minimum of 14" inches.The footing shall be 8” larger than the largest dimension of the post.

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DecksEtc

The posts are inside the perimeter of the deck. The cantilever is 1' all the way around.

I understand codes are different in different areas. My rant was based on the fact they reduced the size of 8 of the posts from 12" to 10" for no apparent reason - why should they care if I use larger footings?

I do undertand the reasoning of the larger base on the center footing from those here that have explained it but I have never had this kind of change made to any permit drawing I have ever submitted. It would be nice if there was some sort of consistancy.

It just never fails to amaze me how they always add some red pen no matter what I submit.

naptown CR

I just ran ,because I am bored, the load calculations on the posts given the design criteria you gave with beams running in 22' direction.

Design loads I used are based on Fairfax County
60 psf live load 15psf dead load assumed soil bearing 2000 psf

the four posts on the corners will require a minimum 13" diameter footing each carries 1608 pounds
The perimeter center posts on long side will require minimum 18" diameter footing each carries 3375 pounds
The perimeter center posts on short side will require minimum 17" diameter footings each carries 2887 pounds
The center post will require minimum 24" diameter footing this carries 5250 pounds

You may want to reconsider your footing sizes unless you are building on rock. I have also never had an inspector turn down a 16" diameter footing when a 12" was shown on the plans.

Windwash

Greg24k,

Is that 8" rule a local code?

I just looked through my IRC 2006 book and was unable to find anything............but its a big book

We don't have the coastal wind codes you probably have.

I usually use 12" tubes belled to whatever the load requirement is for the decks I build here in MN, but have never run across this requirement.

The detail I like to use for decks is generally 2-2xs for beams supported by a 6x6 (either cedar for appearance or PT for lower decks) with a notch for the beam and 2 ss bolts.

greg24k

That is a National code. Prescriptive Residential Deck Construction Guide
Based on the 2006 International Residential Code Footings R403

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Windwash

I've read R403 three times and can't find it, can you be more specific. I also read the prescriptive guide and can't seem to locate it there either.

I thought the prescriptive guide was just an alternative way to meet code. if you only used the prescriptive guide you would never be able to use 4x4s for posts as it doesn't allow them but the IRC does (R407).

Just trying to find the answer.

greg24k

Here is the link for the Perspective Deck Guide

You can use 4X4 post if you place the girder on top of the post, without making a notch in the post. The guide mostly shows a post being notched to accept the beam, where minimum post requirement should be 6x6.

I believe according to most jurisdictions in NJ the highest you can go with a 4x4 post is 5'. I will have to check, I haven't done any decks lately, but i have one coming up.

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