Are flat roofs faster and cheaper than gabled roofs?

In terms of

- construction time

- construction cost

- long term maintenance costs

This is for a commercial structure in the north east (snow!). For the flat roof, we are thinking of using foam (SPF or similar) as the outside sealing material, we hear it creates a near perfect seal that lasts decades with little maintenance. The foam also adds insulation, which is a plus.

Thoughts? Experiences?

Posted By cjbuild on 08 Jul 2011 01:57 PM
Are flat roofs faster and cheaper than gabled roofs?

In terms of

- construction time

- construction cost

- long term maintenance costs

This is for a commercial structure in the north east (snow!). For the flat roof, we are thinking of using foam (SPF or similar) as the outside sealing material, we hear it creates a near perfect seal that lasts decades with little maintenance. The foam also adds insulation, which is a plus.

Thoughts? Experiences?

Metal based SIPs are perfect for flat roof applications, with taped joints they are the , structural component, the insulation and the permanent roof.

http://www.southernsips.com/job_jaxjob.html


http://www.southernsips.com/job_monroebusiness.html

3lb foam is pretty rugged stuff, but I have no long term experience with it in roofing apps. It's an expensive way to add R- I'm not sure if there's anybody with more than about 2-decades of actual experience with polyurethane foams as the primary roofing material. It may need some sort of ballast or other covering to avoid long term breakdown from ultraviolet sunlight. At ~2" or more (R14-ish) it begins to add structural strength to the roof deck as well.

Flat roofs on commercial buildings need the snow-load capacities attended to. Every big snow year in MA (such as this year) there are multiple flat-roof failures and building collapses. (I had to abandon the building where I currently sit so a crew could hand-remove the 4-6' drifts from the roof, which were causing significant visible bowing on the underside of the supporting trusses in places.) We now have a few leak points where they manged to ding the membrane with snow shovels. With an SPF roof those leaks would not have happened.

Yep, I understand we'll have to clear snow off the roof occasionally. But if we save $500k on the roof construction and open a month sooner, it's worth it. Facility is approx 40000sqft, so it's a big roof. We're going to bring it up next design meeting but I wanted your thoughts so we don't sound like idiots.

So will it be cheaper? Faster? ...and if it ever gets financed :/

Big commercial is very different, but I know a couple of residences where flat roofs were eventually replaced with pitched roofs.

Posted By jonr on 08 Jul 2011 05:36 PM
Big commercial is very different, but I know a couple of residences where flat roofs were eventually replaced with pitched roofs.

Why, were they concrete or plywood covered with felt material before they leaked?

John

I don't know the details, just that they kept having problems, so they eventually went to pitched. Both were in cold (ie, snow) areas.

SD Carruthers out of Argyle NY has been using SPF for roofing since the early 70's

If you look around, how many 40,000 sf single story buildings do you see with anything other than a flat roof? Darn few! There is a reason.

I have no first hand experience with polyurethane roofs, but they do need UV protection, need walkways if used to access equipment and are molto brutto . I can imagine that shoveling snow from an uneven surface is difficult.

It is not rocket science to do a good flat roof, but attention to detail is critical.

Bruce
(who would not be disappointed to never shovel snow again)

Thanks for the Argyle NY tip. I'll put them on the list. We may not foam the entire roof, but have them strategically foam flashing/trouble spots.

Before you make a decision, also ask what your heating methods are going to be and can your roof be used for something else in the future such as for solar. The reason I ask is that some very big flat roofs here were recently made into sloped steel roof and the space inside was used as a big solar collector for the new air source heat pump that heated the building and for a reasonable cost they saved a lot of running costs. Just something to think about.

Posted By MikeSolar on 28 May 2012 06:49 AM
Before you make a decision, also ask what your heating methods are going to be and can your roof be used for something else in the future such as for solar. The reason I ask is that some very big flat roofs here were recently made into sloped steel roof and the space inside was used as a big solar collector for the new air source heat pump that heated the building and for a reasonable cost they saved a lot of running costs. Just something to think about.

Just noted the date on this post..............ignore my comments