# Guesstimates?



## Tatnic (May 11, 2009)

Gentlemen:

New poster here. I have a project that I need some help with and I'm glad I found this forum. If someone could chime in it would be greatly appreciated.

My "project" is an older building, *flat* roof, single-ply rubber over perlite and the original built up asphalt. The support structure is 2x8's 16" oc, 1/2 decking, and the ceiling is hung from the same 2x8 joists. Between the joist is fiberglas batt insulation. The roof area is just over 24 squares. 

Portions of the deck are bad and need replacing...I estimate about 4 squares although we won't know for sure until we rip off the old roof and expose it.

I am preparing a report for the client and need a budget amount for a complete replacement (New Hampshire):

1. Remove and dispose of ballast--cost per square=________.

2. Remove old roofing, i.e., single ply rubber, perlite insulation, asphalt, and gravel stops--cost per square=_______________

3. Replace about 4~5 squares of decking that are rotted. Cost per square = _________________.

3. Add and attach new polystyrene foam to provide positive pitch, average thickness is around 2". Cost per square=_____________________.

4. Place a new PVC roof membrane. I'm guessing that plate bonding might be the best bet. Not looking to ballast the roof again...cost per square=____________.

My questions are: 1) How would this roof be ventilated? It currently is not and the structure is not all that condusive to ventilation. 
2) Is ventilation absolutely required or are there other ways to minimize internal moisture problems without ventilating the roof structure? I am proposing ACX plywood whereever we replace bad decking (which rotted from past leaks through the old asphalt roof).

3) I'm not a roofer, so if you have a better way to approach this problem, then please share. And again, thanks for any budget figures you can provide.

Tatnic


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## Grumpy (Oct 29, 2008)

4 hundred forty two million bajillion pesos. 


You are preparing a report for the client. What is your professional role in the equation? What ever pricing we give you is meaningless based upon real world values and local micro economic variables. 

Ventilation is not absolutely required on low slope structures, at least I have never seen it in a spec except on recovers. In these cases they make breather vents specifically engineered for flat roof applications. There are one way and two way breather vents. I just bid a job very much the same as what you described, minus the ballast. One other roofer was giving her a song and dance about ventilation so I suggested some breather vents be installed as part of the roof assembly after we have verified the ceiling is indeed insulated.

Why would you use ACX (sanded) plywood? It will not be visible from the under side and CDX would be more cost effective without sacrificing any quality.


If you want some numbers I am going to need some more information. What is the height from ground to roof edge. What is the access like? Can dump the garbage right into a dumpster or will I need to wheelbarrow it to the street? Will a chute be needed? What about delivery, roof top by crane or will it need to be man loaded? What type of PVC? You want us to taper the roof with insulation, we need a detailed roof plan. Any drains, gutters, edge metal?


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## Ed the Roofer (Sep 15, 2008)

As an Engineer, you know already that there are many variables to consider.

You may only wish to play the role of specifier, but conditionally allow options to be revealed for efficiency and cost savings along with additional life cycle productivity.

I feel it is foolhardy of you to suggest pricing to your clients where you have no installation experience nor regional source to request pricing variables from.

Would your client consider a well known contractor providing the specifications and anticipated costs, or even a Certified Roofing consultant?

Ed


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## Tatnic (May 11, 2009)

thanks Grumpy,

18' high, good access (crane accessible), but would need a chute to convey the old ballast. Dumpster for the other waste would be fine.

CDX yes...typo.

Assume roof is easy, flat surface, which it is. Pitching it to the edges (or hip style) is doable (after removing the gravel stops).

Right now the total roof structure (from the gypsum ceiling to the top of the rubber) is only 10.25"...not alot of room to work with, and there's batt insulation laying right on the gypsum ceiling. Given the fiberglas location, we really may not be able to do much.

thanks again.


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## Grumpy (Oct 29, 2008)

Our hourly rate is higher than the typical for my area, and I have no idea what hourly rates are in your area. I'll give you aprox production rates though. To remove the gravel I'd figure one man hour per square on the roof and depending where it needs to go by wheelbarrow perhaps another man hour on the ground

For the tear off of what you described (single ply roof over asphalt roof) I'd guess it'd take 2 man hours per square assuming the garbage goes directly into a dumpster without needing a wheelbarrow.

Decking at a cost of $65 per 4x8' sheet of 1/2" cdx 4 ply. 

Polystyrene at about $160 a square off the top of my head for 2" 1 lb density. Although I prefer PolyIso which is only slightly more money and has a higher R value. However if the ceiling is insulated, is it really necessary to insulate the roof? This does not include any taper. Iso is about $76 a square for material and can do a square an hour.

Pvc is about $270 for a 9 square roll. If it's a wide open roof that 9 square roll will take less than 6 man hours to install. On small jobs like this man hours always increase. 


All said and done you are looking at $650 a square to my pricing. That's making alot of assumptions and does not include rotten wood.


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## Tatnic (May 11, 2009)

Ed the Roofer said:


> As an Engineer, you know already that there are many variables to consider.
> 
> You may only wish to play the role of specifier, but conditionally allow options to be revealed for efficiency and cost savings along with additional life cycle productivity.
> 
> ...


I have already asked a local roofer for a quote, but he may be overly optimistic during the quoting process (things are tough around here). I would rather give them a good budget number and have the bids come in around it than to use a low figure and have egg on my face afterwards. I did a back of the envelope estimate and came up around 700/square...which is right around grumpys, so I'm in the ballpark.

So what about rubber in a lighter color? There's not much insulation and the folks on the top floor suffer during the hotter months. But if we're installing a pitched poly substrate, is color as important from a solar gain perspective?

thanks guys....great site.


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## Ed the Roofer (Sep 15, 2008)

You would be much better off with a White PVC alloy membrane roof that gets heat welded seams instead of White EPDM.

In California, IB Roofing Systems would be a well known material.

How close are you to L.A.?

Ed


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## Tatnic (May 11, 2009)

Ed the Roofer said:


> You would be much better off with a White PVC alloy membrane roof that gets heat welded seams instead of White EPDM.
> 
> In California, IB Roofing Systems would be a well known material.
> 
> ...


about 2,000 miles. In New Hampster actually....right coast. Our biggest problems in the winter are ice dams, and this roof needs to be light colored and better insulated since its going to be impractical to add any ventilation. Is that membrane ok for colder climates or are there better choices?

thanks


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## Ed the Roofer (Sep 15, 2008)

I apologize. For some reason, I had it stuck in my mind that you were on the West Coast in California somewheres. 

Yes, the 80 Mill IB Roof System would be very durable in winter conditions.

A friend from Schindler Roofing out of Utah swears by it and they have pretty extreme winters in his area.

The white reflective properties are a tremendous energy saver, without requiring maintenance. Also, if add on or repairs ever need to be done, it is quite easily repaired with an electric hot air heat welder gun and a scrap of material.

Ed


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## Tatnic (May 11, 2009)

Ed the Roofer said:


> I apologize. For some reason, I had it stuck in my mind that you were on the West Coast in California somewheres.
> 
> Yes, the 80 Mill IB Roof System would be very durable in winter conditions.
> 
> ...


Thanks Ed...I'll check it out.


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## Tatnic (May 11, 2009)

How would this typcially be attached to the roof structure? 

1) Would it be mechanically fastened down through the eps insulation into the deck? Or
2) would it be adhered to the poly which is mechanically fastened to the deck?
3) Or maybe the poly is mech. attached and the membrane is also mech. attached to the deck?


thanks.




Ed the Roofer said:


> I apologize. For some reason, I had it stuck in my mind that you were on the West Coast in California somewheres.
> 
> Yes, the 80 Mill IB Roof System would be very durable in winter conditions.
> 
> ...


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## Ed the Roofer (Sep 15, 2008)

Mechanically attached typically. I am not familiar enough with alternative securement methods allowed by them, but fully adhered might also be allowed.

Ed


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