Room addition for "partially enclosed" building in Florida 1

[SSEngr]

Anyone in Florida who is designing additions or renovations to existing buildings (commercial or residential) may be in for a bit of confusion at the building department.

I'm aware of the new law in Florida that will require all new buildings in the debris impact regions to be "enclosed" per ASCE 7 (ie, use impact rated glass or shutters). But consider the following: an addition or renovation is proposed for an existing building where there is no documentation available to prove the existing windows are impact rated and there are no shutters AND it is not required to bring the existing building up to code (ie, do not have to replace existing windows or add shutters because the scope of the renovation does not trip the threshold to do so).

I fully agree that any new glazing installed in an addition or renovation should be impact protected. However, the design pressures for analysis of any new components or cladding should be based on a "partially enclosed" condition for the above scenario and use the higher +/- 0.55 coefficient for internal pressure instead of the +/- 0.18 coefficient. This is because the existing windows could break, thus creating the "partially enclosed" condition for the entire building, including the new addition or renovation.

The building department here in Cape Coral, FL is not allowing this! They are insisting that the existing building be treated as "enclosed" because of the following reasoning - and this is a quote - "the existing building was never designed to withstand the 'partially enclosed' condition, therefore, you must consider it to be 'enclosed'". I think they are misunderstanding the concept, but I have not been able to convince them otherwise and they say that at least 3 local engineers agree with them! They went on to say this will all be a moot point in July when the new law goes into effect because then all new additions must be designed as "enclosed" because "partially enclosed" will not be allowed anymore.

The wording in this new law is getting people very confused.

Please tell me if I'm wrong, but, according to ASCE 7, the Enclosure Classification is evaluated strictly by the percentage of openings in the walls. The Classification has nothing to do with the structural integrity of the building. It is simply one of many variables that are needed to arrive at the design pressures which can then be used to either analyze the existing structure or design the new structure.

I designed a residential room addition for the 0.55 coefficient, and stated on the plans the structure is "partially enclosed". But the bldg dept is not accepting this and saying I must state that my design criteria is for 'enclosed'. They are being pretty strong about this and won't issue a permit otherwise. As all engineers know, we can't submit sealed plans with incorrect design criteria!! What to do?? Where can I turn to get an official ruling on this?

 

[DonPhillips]

You can adjudicate it to the local appeals board. Another option is to locate another authority who agrees with your interpretation and you can ask the two building officials to meet with you to discuss.

Don Phillips

http://worthingtonengineering.com

 

[scottiesei]

I understand what they are saying though. I have been involved with several little battles like this over the years, especially on additions. For some reason the plans examiners that get the "little" jobs feel like they have something to prove and hammer them for every little thing. They should not nail you for over design in their eyes though. If you do alot of work there, I would try not to make this small issue a battle, rather figure out a way around it. I.E: Design the addition as "fully enclosed" but note that an additional safety factor had been included due to the scenario which you just stated and use those numbers in your calcs. You are just wanting to ensure the structure is safe and that you are protected, who cares what it is labeled as long as you design it for what you feel is correct. Good luck!

 

[scottiesei]

Oh, and document the assumptions in your files!

 

[csd72]

This is fairly typical with authorities, the people who are checking your plans basically have a ticklist and they do not always fully understand the implications.

The solution is a matter of wording.

"This design exceeds the requirements for a fully enclosed condition"

or something to that effect that gives them their word to tick off but does not tell a lie.

 

[SSEngr]

Thanks to all for the replies. Yes, it's unfortunate that these little jobs cause such a big fuss. I won't make a big deal out of it, but it's just the tip of the iceberg, so it would be nice to get their thinking straight. I did reach an agreement with the plans examiner to just get this one job dislodged, but his thinking has not changed. I'm going to round up some support and have a meeting later, which has proved to be effective on other matters in the past.

Meanwhile, my concern is not so much for my design (thanks for all your advice on the wording, etc.), which is easy to be conservative in small houses, but rather with window selection and the roof truss engineering. Windows are handled by showing the +/- design pressures at each window location on plan. But the roof truss guys only have a toggle switch in the software for "partially enclosed" or "enclosed". I'd like them to run it as "partially enclosed" to use the higher uplift pressures, but if my plans say "enclosed", that's the way they will run it. I can select stronger strapping to compensate, but the actual trusses won't be designed correctly. I realize on a small room addition the trusses will have lots of excess capacity, but, it might be otherwise on a bigger job.

Any ideas how to handle the truss design issue?

 

[CFSEng]

I'm not sure I completely follow your logic. If you are not doing any modifications / enhancements to the existing structure, why would you design the addition for larger pressures when you are attaching the addition to the existing structure? Or are you designing the addition to be self supporting and not rely on the existing structure for support?

 

[SSEngr]

CFSEng, since the addition is connected internally to the existing main house by open doorways, it becomes part of the total envelope and it will experience the same internal air pressures as the main house. So even though we are putting impact windows on the new addition, the existing house does not have impact windows, and thus could break, which leads to the higher internal pressures throughout the entire structure, including the addition. If higher pressure gets created in the existing portion, it will quickly equalize into the addition (ie, the addition is not sealed off from the main house - you can walk through open doorways).

Putting it another way, what if the so-called addition was always part of the original house, and all we did was replace the windows in that room with impact windows, or to exagerate, closed in all the windows in that room. It would still experience the same internal pressures as the rest of the house.

Does that help clarify?

 

[csd72]

Say on the drawings that All trusses to be designed for the worst case of partially enclosed or fully enclosed.

The plan examiners might not know which is the worst case, but they cant argue against this statement.

 

[CFSEng]

SSEngr,
You stated my point, the entire house (old and new) experience the same internal pressure. So is the old part of the house able to withstand the partially enclosed pressures?

My point is why would you want to design a new very strong addition when the rest of the house will blow down during a hurricane and only your addition is left standing.

 

[SSEngr]

CFSEng,
Your point is well taken and the existing house may indeed blow away, but the Code does not require us to check it, as long as the new addition does not do anything to compromise the existing structure. But we still must make sure the new impact windows and the new roof trusses are designed for the higher internal pressures for "partially enclosed" situation. That's really the only issue I'm battling is how to make sure that happens - and the plan examiner is saying I'm not allowed to. Here's why:

Keep in mind - this is only an issue for small room additions on old houses with no impact protection.

There is an new law coming in Florida that states:
A) all new construction must provide "wind-borne debris protection".

The problem arises because the Building Department is interpreting this to mean:

B) "you can no longer design for the 'partially enclosed' condition".

I have seen this exact wording in a memo that is circulating.

They just don't get it. They took A) and turned it into B) which is 2 completely different concepts.

I just found out that other nearby building departments recognize the special situation for small room additions and are accepting "partially enclosed". I guess it's just my local guy in Cape Coral.

 

[CFSEng]

My understanding is based on the old law, the design engineer had two choices:

A - have impact protection and design as enclosed
B - no impact protection and design as partially enclosed

The new law no longer allows option B (i.e. you can no longer design for the partially enclosed condition) so your only choice is option A. (These options and revisions apply only to the wind borne debris region which Cape Coral is in)

So it sounds like their wording is close "you can no longer design for the partially enclosed condition" but it needed to have added "in order to avoid the use of impact protection"

But back to my original point, if I hired you to design a house addition, I would question why your design costs me hundreds (or thousands) of dollars more in construction costs because you want the addtion to be overdesigned in comparison to the remainder of my house. I guess thats your decision to make.

Good luck with the building department

 

[csd72]

CFSEng,

You should actually read posts before you may such critical statements. It appears to me that you have completely misunderstood the whole lot.

If the existing building does not have the necessary impact resistance e.t.c. then it must be treated as partially enclosed.

The extension that is attached to the existing building will have the same internal pressure (i.e. a partially enclosed pressure) regardless of how its walls are designed. In reality it is slightly worse if the extension is fully enclosed but the code doesnt really take this into account.

SSengr's point is that because of the above points he knows that the internal pressure is that of a partially enclosed condition but the local Authority is saying it must be designed for fully enclosed. That is the dilemma.

It is the local authority that is making him spend his clients money unecessarily on fully enclosed windows that achieve no benefit.

 

[SSEngr]

"in order to avoid the use of impact protection" - yes, you hit it right on the head there. That's what they needed to add.

Regarding your last paragraph, it's not me who wants it to be designed better than the existing house. If not for the new law, I would give you the option to design the new addition for regular windows and be partially enclosed and save you lots of money. What's the point of putting in impact windows in the addition, if all the other windows in the house can break out. The fact that the new law requires the addition MUST use impact rated windows, that's what costs all the extra money.

The design elements that I'm concerned about only cost a few dollars more (probably not more than $10 extra). It's more a matter of being technically correct on sealed documents. Since your old windows can break, then your new roof will receive extra uplift due to higher internal pressures and I want to make sure it is strapped down adequately (and if the roof was bigger, I'd want to make sure the truss itself was designed for the higher uplift so that one little gang nail plate somewhere won't pop off - it's just pennies for a bigger plate in a few key joints). And your new windows, even though they are impact rated, will receive extra pressure, so I want to make sure they are fastened correctly so the whole frame does not blow out. All we are talking about is a few upgraded straps at the roof and maybe some extra screws at the windows. The changes are relatively minor.

Let's just say for example that I designed the new addition for the lower pressures of "enclosed". Then a storm hits, breaks windows in the existing house (nothing else is damaged) and then one of the NEW windows in the addition blows out of the window bucks because I did not specify enough screws. Who's in a pickle then? All for an extra 25 cent tapcon.

So you see, it's just a few dollars more in construction. But more importantly, it's the protection of ones PE license.

 

[CFSEng]

SSEngr,
In my opinion, there would ultimately be more than $10 worth of cost but that's just my opinion. I guess I'm thinking of the possible increase in footing size for uplift, wall stud size for increase in bending, attachments of wall framing to ground and roof may increase, additional uplift anchorage, possible increase in lumber grade for trusses, etc. You can see where I'm going with this.

Anyway, as my final point noted, it ultimately is your seal on the line and you need to be the one to sleep at night so good luck with the building department and convincing them you are right. Maybe you can talk with the person who originally wrote the memo you saw circulating and try to convince them to issue a clarification

My comment to csd72 is you state 'If the existing building does not have the necessary impact resistance e.t.c. then it must be treated as partially enclosed.' This is an incorrect statement if:
1) the original structure was built prior to the ASCE 7-98 requirement of the wind-borne debris region
and
2) per the original post of SSEngr "...AND it is not required to bring the existing building up to code "

Maybe you should have read the original post more thouroughly

 

[SSEngr]

CFSEng,

Yes, all those things might be a concern, but, I guess I should have given more details to this particular job. The walls are only 8' high, 8" masonry with 8"x16" concrete tie beam at top, all w/ rebar (this is standard construction here - nobody uses wood studs on first floor). The max roof truss span is 17 feet (I confirmed w/ truss engineer there is no change at all to the truss lumber or nail plates - only the resulting uplift). We always embed a Simpson META16 strap in the concrete tie beam as the typical anchorage at each truss - this has 1450 lbs allowable uplift and it's the cheapest strap you can buy (of course we use bigger stuff at girders as needed). The truss sits directly on the concrete tie beam with an isolation plate (there's no wood sill like up north). So basically it's a little bomb shelter. When we compared the truss uplifts for "partially enclosed" vs "enclosed", only one truss increased enough to exceed the 1450 lbs, so we just put 2 meta16 at each end. That was the only actual change for the entire project - adding 2 extra straps. I've been doing this for long enough that I knew it would be that way - almost trivial.

I happen to agree with CSD72 'If the existing building does not have the necessary impact resistance e.t.c. then it must be treated as partially enclosed.' You must evaluate what you are dealing with here and now, not what somebody did in the past. If the window can break, it can break - I really don't want to go over to the guys house and toss a coconut at his window to prove the point.

Lets look at the real issue here: The only thing that is relevant, from a professional engineering standpoint, is to correctly calculate the wind pressure that the new room addition will experience. Period. How does one go about doing that? You must determine the pos. and neg. interior pressures and pos. and neg. exterior pressures. The first step then is deciding what coefficients to use. For the interior, it's either +/- 0.18 or +/- 0.55. If the old windows can break (regardless of what you call it), you must use 0.55. How can you say that using 0.18 is the right thing to do? Regardless of the semantics, I have every right to elect to use the more conservative +/- 0.55, especially knowing from years of experience that the real increase in construction cost will be less than $10. My sole purpose for starting this discussion was because I'm up against some Plans Examiner who is telling me I'm not allowed to do this.

Anyway, the permit is issued, the Plans Examiner still has his head in the sand, the addition is designed correctly, and the customer is the proud owner of 2 extra straps.

I rode out hurricanes Charlie and Wilma. The eye of Charlie passed 15 miles from my house. Until you actually experience it first hand, it's hard to appreciate the forces. I watched the shingles peel off my neighbors house and plaster against my sliding glass door. I watched my pool screen enclosure self destruct and nearly rip the eaves off my house while the aluminum framing swung against the windows. I watched tree limbs, awnings and who knows what go flying past. On my neighbor's house, the vinyl soffit blew out at the eaves and the rain drove in horizontally into the attic, soaked the insulation and collapsed the drywall ceiling - how about that! It's very very real. And it's wrong to do a dis-service to a customer to "save" him money by possibly underdesigning his new structure.

I'm going to sign off from this thread now. Thanks to all for the input and the lively discussion!