Permanently frozen ground ???

[jeffk]

I'm building a simple 20'x20' deck (12" above ground) that will not be attached to the house. Code says I need footers 12" min below ground & I would be excluded
from frost protection depth. I live in PA so from what I understand my footers would need to be somewhere between 12" & 36" deep to comply with
building code. My question is; what does it mean "Footings shall not bear on frozen soil unless such frozen condition is of a permanent character".
Does that statement void the exclusion and would the footers still need to be 36" deep?

I'm also considering looking at using the deck block system (http://www.deckplans.com/how-it-works) and curious if this type of deck structure would be acceptable according to the building code. If not; what would be the issues? Your concerns?

Thanks for your help,
Jeff

[Jerry Peck - Codeman]

Hi Jeff,

I'm building a simple 20'x20' deck (12" above ground) that will not be attached to the house. Code says I need footers 12" min below ground & I would be excluded from frost protection depth. I live in PA so ...

Does PA use the IRC (International Residential Code), a code based on the IRC, or one similar to the IRC?

I ask because in the 2006 IRC there is exception to minimum footing depth and frost protection, and that exception covers precisely what you are building:
- 3. Decks not supported by a dwelling need not be provided with footings that extend below the frost line.

If the exception applies to your code, that will solve your problem.

Now to answer your questions.

My question is; what does it mean "Footings shall not bear on frozen soil unless such frozen condition is of a permanent character".
Does that statement void the exclusion and would the footers still need to be 36" deep?

No, that section is addressing structures constructed in the permafrost regions where the soil is ALWAYS frozen, thus there is no need to address soil movements from when the soil thaws out - it NEVER thaws out. Think northern parts of Canada, the Arctic, and the Antarctic, possibly parts of Iceland - but not to worry, that does not apply to PA.

I'm also considering looking at using the deck block system (http://www.deckplans.com/how-it-works) and curious if this type of deck structure would be acceptable according to the building code. If not; what would be the issues? Your concerns?

First, *IF* your code has the exception from footing depth and frost protection as stated above in the IRC, and ONLY *IF* you code has that exception, and PROVIDED that your deck was not attached to or supported by the house in any way, shape or form, then you may be able to use those pieces.

Note that I said "may" "be able to use those" as many areas of the country have uplift tie-down requirements and those pieces are not going to meet uplift resistance requirements - whether or not the deck is attached to the house.

The exception from footing depth and frost protection is only an exemption from those two things, not any other requirements.

Most area have requirement to anchor the structure down as you do not want it blowing around and becoming air-borne projectiles and debris.

Additionally, those pieces offer no resistance to sliding (such as high winds pushing against the deck and sliding it across the soil) as they are not buried in the soil to resist such forces.

If you construct any vertical surfaces on the deck, such as backs to benches, those can catch high winds and create additional forces on the deck in addition to uplift, such as the sliding I mentioned above and overturning (where the wind is trying to lift the deck and overturn it by applying force against back of the bench.

Those pieces are sold in the Big Box stores, but that does not mean the code allows them to be installed. Those are one of many items which are allowed to be manufactured, sold, bought, just not allowed to be installed ... "not installed" in most uses they are installed for. Those pieces are allowed to be installed provided all the right conditions apply: 1) deck is not attached to the house (you meet that); 2) does not require uplift resisting straps (you may, or may not, meet that - you would need to contact your local AHJ - Authority Having Jurisdiction - i.e., your local building department.

End result is you MIGHT be allowed to use those, but I would doubt it as they provide no uplift resistance. I grew up 40 miles south of Buffalo, NY and there are high winds in the winter blizzards there, thus the requirement for uplift resistence is likely. I am in Florida now and have been the last 50 years and we have those "high wind events" (those things called "hurricanes") and definitely need to tie structures down with proper uplift resisting straps.

[jeffk]

Hi Jerry,
Thanks for your excellent reply!

Another question or two or three . . . if you don't mind?

Let's assume that the proposed deck would meet the frost protection exception here in PA,
beams, joists, footers & spans would also meet code requirements and a deck-block structure can be tied down.
Would all 3 structures shown below be acceptable ways of constructing a deck?

Deck_Support_Options.jpg

Since we're 'stickin' to the code'; what would be the prefered option/method?

I would also like to know if beam ends can be angle-cut/joined where the bearing ends sit on
the same column/footer as shown in top & bottom image below?
Which one would be the prefered method, assuming beam size & spans are acceptable?

FrontEndBeamOptions.jpg

Suggestions for supporting the front end would also be welcomed if the above are not up to snuff.

Thanks once again for your time,
Jeff

(Tried to load some nice 3D pdf files but wasn't allowed, so added jpg's)

[Jerry Peck - Codeman]

Hi Jeff,

Let's assume that the proposed deck would meet the frost protection exception here in PA,
beams, joists, footers & spans would also meet code requirements and a deck-block structure can be tied down.
Would all 3 structures shown below be acceptable ways of constructing a deck?

See below:

Deck_Support_Options_01Annotated.jpg

I would also like to know if beam ends can be angle-cut/joined where the bearing ends sit on
the same column/footer as shown in top & bottom image below?

Yes. That is the way it is done.

Which one would be the prefered method, assuming beam size & spans are acceptable?

Like this:

Deck_Support_Options_02Annotated.jpg

You do not want to use the 'Xed' out method as you want to tie the perimeter beams together for rigidity and for keeping the structure together. You will want to use proper straps and tie-down anchors to secure everything in place.

(Tried to load some nice 3D pdf files but wasn't allowed, so added jpg's)

Yep, I did not realize this forum software did not allow pdf files to be uploaded until after I had it set up and running, I wish pdf files could be uploaded.

[jeffk]

Jerry,
Thanks once again for your help!

To reduce the "failure to do" scenarios with deck attachment to the house, would attachment of ledger board to the
concrete foundation be a better option than attaching to the rim board of the house? The deck would be low enough
to the ground to accomodate a foundation attachment.

Figure15_AWC.jpg

For house attached deck, why would the footings need to be at the depth of the footings for the house? Isn't frost depth (36" for PA) enough?
Assembling beams & digging footers 36" deep or deeper would be minuses.

Would the settling issues be enough not to consider the free floating w/12" deep footers?
Assembling beams would be minuses. Digging footers to 12" deep would not be bad.

Leveling for deck block structure would be to add 4x4 posts into each row of blocks and strike a line. Cut as needed. A little tedious but not bad.
Shims could be added as needed as settlement occured.

leveling.jpg

Costs for the 3 structures would be within $50-$100 of each other. $5 for a deck-block.

Would you still cross out the deck-block structure?

If you were up here in PA which structure (for a ground level deck) would you like to see a homeowner utilize?

Thanks,
Jeff

[Jerry Peck - Codeman]

Hi Jeff,

Attaching the ledger to the poured concrete or solid filled masonry (not hollow masonry) foundation wall would work as long as the flashing was let into the wall above and brought down and over the ledger to keep as much water off the ledger as possible. That would replace where the drawing states "to resist corrosion and decay, this area should be caulked" as caulking is not going to seal that area well at all.

The other thing to consider when installing a deck down there is the step height up to the interior spaces. You would want a finished deck height to interior floor height of no greater than 7-3/4 inches, and I would design around 7 inches or 7-1/2 inches to allow for errors which would still meet the maximum of 7-3/4 inches riser height. Thus you could measure down, allowing for the deck flooring to be: 7 inches; 14 inches; 21 inches; etc.; down, keeping in mind that the stair would need to be as wide as the door (as wide as a double French door or a sliding glass door including fixed panels) and that four or more risers requires a handrail.

Also keep in mind that you may be carrying food from the house to the deck and that stair could contribute to a fall.

Regarding the other question about the depth of the deck footings, I presumed the house footings are 12 inches below frost depth, which is also where the deck footings would need to be.

If the house footings are more than 12 inches below frost depth, the deck footings would only need to be at 12 inches below frost depth.

The settling issue with the free floating deck on those block could be corrected with shims, however, by the time you realized there was a settling problem, the wood would have taken the new bowed shape. You would be creating a future maintenance issue which would not be addressed in the timely manner needed, and as your drawing shows, unless the deck was high enough, how would you even be able to crawl in and access those blocks for shimming? Not as you drew that drawing.

Yes, I would still cross out the deck-block structure.

Which would be best to utilize? Either of the two which are not crossed out.

[jeffk]

Hi Jerry,
As usual, very nice response!

AHJ was at the house today. He insists that all footers (whether deck is attached to house or not) need to be below frost depth.
Exception 3, (and the other 2 as well), he feels are voided by the "permanently frozen ground" sentence. I think he's wrong but no use fighting.
That's why I was asking for some clarification on the sentence in the first place.

He definately didn't like the deck-blocks. So I'll be going with the attached method.

The inspector said the deck footers will only need to be 12" dia @ 36" deep. I don't feel comfortable with his recommendation.
I feel they should be sized a little larger. Would you look at my design and provide some feedback on the questions below?
To help with my calculations, I used the guide from the American Wood Council.http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf
Seems like a very thourough document.

Questions about design:
Should the beams be (2x)2x8's or (3x)2x8's based on pier spacing? I have the latter.
Should the footers be 12" dia. like the inspector suggested? Or larger like in my design?
Can the 2 footers for the step area (upper left of deck) be smaller than 12" dia.?
Can the steps (only one step up to deck) rest on the ground as suggested by inspector or should I go to 36" deep as well for footers?
Step stringers then to bolted to posts extending up from footer. Is this overkill or correct?

Well that should get me started.

Thanks once again,
Jeff

DeckSupport.jpg

DeckIso.jpg

[Jerry Peck - Codeman]

Hi Jeff,

I haven't missed or forgotten about your post, I just need to make sure I have the time to go over everything and reply with the correct information, hopefully tonight.

Also, I do not do engineering so I will not be "designing" your deck, only pointing out what I see not quite right. If I were an engineer I would still not be able to design it your deck as I would need to be licensed in your state, and if licensed in your state, the engineer would not design it for free anyway - that is how the structural engineers make their living.

Looking forward to spending some time and going over your information and the code and pointing out things I see which are not quite right, if any.

[jeffk]

Hi Jerry,
Hopefully I designed it correctly (Graduated from PennState with Mechanical Engineering degree back in '83).
Hope I didn't burn out too many brain cells sinse then.
Just want to make sure the structure (beams, footers, joists) are adequate to meet code.
Didn't feel totally comfortable with some of the inspector's recommendations.
I'll will be incorporating all of your previous suggestions as well.
One change I made was to shorten the span on the front beam (previously 9'-0") now 8'-10".

Thanks and looking forward to your comments,
Jeff

[Jerry Peck - Codeman]

Hi Jeff,

Yep, the AHJ does have the final say and it is easier to work with them then to fight them - unless the fight was over something well worth it.

Q. Should the footers be 12" dia. like the inspector suggested? Or larger like in my design?
- The footings can be larger, yes.
- Your beam span is shown as 8 feet 6 inches and your joist span is shown as 10 feet.
- The http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf is a very good document and it shows, on page 9, Table 4. Footing Sizes, shows that your beam span of 8 feet 6 inches exceeds (first column in table) the Beam Span of 8 feet, thus I would recommend going down to the 10 foot Beam Span row, which shows a 19 inch diameter footing 7 inches thick. I've never liked footings less than 12 inches thick minimum myself, but then I am a General Contractor who liked to over build when possible.
- Note 1 in Table 4 states that you can reduce the diameter by 2 inches and use that for the sides of a square footing, thus I would recommend using an 18 inch by 18 inch footing (I know, 2 inches less is only 17 inches, but I like 18 inches better).

Q. Should the beams be (2x)2x8's or (3x)2x8's based on pier spacing? I have the latter.
- You did not state, or I missed it, the species of wood you are using, so I will address both groups in Table 3. Deck Beam Spans on page 5.
- SYP (Southern Yellow Pine): 2-2x8 with 10 foot joist spans = beam spans of 7 feet 1 inch, and you are showing 7 feet 6 inches - NOT GOOD.
- SYP (Southern Yellow Pine): 3-2x8 with 10 foot joist spans = beam spans of 8 feet 11 inch, and you are showing 7 feet 6 inches - GOOD.
- SPF (Spruce Pine Fir): 2-2x8 with 10 foot joist spans = beam spans of 5 feet 4 inch, and you are showing 7 feet 6 inches - NOT GOOD.
- SPF (Spruce Pine Fir): 3-2x8 with 10 foot joist spans = beam spans of 7 feet 7 inch, and you are showing 7 feet 6 inches - GOOD (BARELY GOOD).

Q. Can the 2 footers for the step area (upper left of deck) be smaller than 12" dia.?
- No, the footings would need to be at least 12 inches square, based on the Wood Deck Construction Guide those footings should be a minimum of 15 inches diameter, or, less 2 inches for 13 inches square. Again, I would always go 12 inches thick minimum for footings.
- Keep in mind that those two footings are within 5 feet of the house wall and the Wood Deck Construction Guide states, in all cap letters "DECK FOOTINGS CLOSER THAN 5'-0" TO AN EXISTING EXTERIOR HOUSE WALL MUST BEAR AT THE SAME ELEVATION AS THE FOOTING OF THE EXISTING HOUSE FOUNDATION."

Q. Can the steps (only one step up to deck) rest on the ground as suggested by inspector or should I go to 36" deep as well for footers?
- The stairs are required to have footings, which should be to the depth required for all footings, and, if within 5 feet of the house wall, see all cap comment I quoted at the question above from the Wood Deck Construction Guide.

Q. Step stringers then to bolted to posts extending up from footer. Is this overkill or correct?
- Go to page 19 in the Wood Deck Construction Guide. Stair footings are addressed there, along with attaching stringers to posts on the footings.

[jeffk]

Hi Jerry,
Thanks for the detailed info!

I will be using SYP.

Is the statement ""DECK FOOTINGS CLOSER THAN 5'-0" TO AN EXISTING EXTERIOR HOUSE WALL MUST BEAR AT THE SAME ELEVATION AS THE FOOTING OF THE EXISTING HOUSE FOUNDATION" a code requirement or a best practice at this time? What methods are used to create a footer hole 9' deep?

Could you provided some help with Table 5 "Fastener spacing" to determine fastener spacing for anchoring the ledger board to solid concrete?
Would I use the 1/2" DIA. bolt & 10' or less joist to arrive at 34" OC spacing?

That's it for now!

Thanks,
Jeff

[Jerry Peck - Codeman]

Hi Jeff,

Is the statement ""DECK FOOTINGS CLOSER THAN 5'-0" TO AN EXISTING EXTERIOR HOUSE WALL MUST BEAR AT THE SAME ELEVATION AS THE FOOTING OF THE EXISTING HOUSE FOUNDATION" a code requirement or a best practice at this time?

Sort of both.

The document you referenced states "Based on the 2006 International Residential Code" and attempts to clarify and simply the code requirements, assimilating the various code sections into an easier to use construction document.

The 2006 IRC states: (underlining and bold are mine)
- R403.1.7.2 Footing setback from descending slope surfaces. Footings on or adjacent to slope surfaces shall be founded in material with an embedment and setback from the slope surface sufficient to provide vertical and lateral support for the footing without detrimental settlement. Except as provided for in Section R403.1.7.4 and Figure R403.1.7.1, the following setback is deemed adequate to meet the criteria. Where the slope is steeper than one unit vertical in one unit horizontal (100-percent slope), the required setback shall be measured from an imaginary plane 45 degrees (0.79 rad) to the horizontal, projected upward from the toe of the slope.

Your slope is greater than 100-percent (greater than 1/1), your slope is "vertical" at the wall of the basement. Thus you would, by the above code section, need to take the depth of your basement wall and its footing, let us use 6-1/2 feet down for the wall and another 1-1/2 feet down for the footing for a total of 8 feet down. Those footings would need to be outside the 45-degree angle above the bottom of the footing, i.e., 5 feet away from the wall at feet up from the basement wall footing bottom, which would mean the deck footings, in your particular instance at a depth of 3 feet to the top of the footing and 1 foot for the footing depth, could be 4 feet from the basement wall and be at that 45-degree angle up from the bottom of the basement footing.

That document is taking other instances into consideration and adopting the position of staying 5 feet from the basement as a good general statement to use to stay clear of, and not intrude into, the code required clear area.

Being as you are constructing your deck to that document, I would not recommend deviating from that document, if you do, then you set yourself up for NOT being able to use that document to support your construction during inspections and discussions with the AHJ ... 'I used this document to construct my deck to and it is based on the 2006 IRC ... well ... except for a few changes I made where I deviated from the document as the code allowed me to.' ... with that statement you will be dead in the water and have no substantial documentation to support what you did and why.

Could you provided some help with Table 5 "Fastener spacing" to determine fastener spacing for anchoring the ledger board to solid concrete?
Would I use the 1/2" DIA. bolt & 10' or less joist to arrive at 34" OC spacing?

The row you are looking at in Table 5 is for "bolts", meaning "through bolts", which are the strongest connection. The row you should be looking at in Table 5 is for "lag screws" as there is not a separate table for concrete or masonry anchor spacing. Thus Table 5 shows that your up to 10'-0" joist span off the ledger would 18 inches center-to-center spacing for the ledger anchors, staggered as shown in Figure 19. Again, because you are using this document as your construction guide you should adhere to the document.