Before you clean off an old flat roof...

21 Replies

Well I think I kind of hit the jackpot...One month into a new rental purchase, I have to bite the bullet for a new roof, a subterranean termite treatment and a drywood termite fumigation.

Property has a flat roof, traditional 2 ply asphalt, with multiple patching over the years, I know the roof is near the end of it's life, and may even been living on borrowed time.

When we inspected the property there was just so much leaves on the roof, that it was holding up a "mat" of leaves sitting there for years and with the south florida rain and sun, those leaves have turned into compost.  Under the new leaves is an inch or two of composted organic matter, I am sure it's good for planting, because there were plants growing out of it.

After I closed, I had a company come by to clean the roof.  They used a giant push broom to push all this stuff off the edge of the roof.  The result is a pile of wet mushy debris about 9 cubic YARDS in volume!

When we used a garden hose to hose off the roof, the next day one tenant called and said the roof's leaking in one bedroom, and another tenant called said they have a leak by the kitchen...there was absolutely no evidence of leak, no stain whatsoever inside, and tenants both said there wasn't any leak since they moved in.  Not even during the rainy summers.

The only explanation I can think of, is this thick mat of disintegrated leaves and debris had been acting as the top layer of the roofing membrane, and once we cleaned it all off, the old roof below started to leak.  A week later we had some additional showers in the afternoon, and the leak continues.

As I got estimates for repairs and reroofs, I noticed termite droppings inside along some baseboards, and one tenant told me about occasionally spraying of "coffee ground" looking pellets in the closet shelves, so I started to get estimates from termite control companies for fumigation, while one company looked around inside and outside for evidence of drywood termites by observing kickout holes and pellets, he noticed one interior door was totally hollowed out...Poking a hole into it, a a few live moving subterrainean worker termites fell out, inside are some mud tubes.  Oh boy.  I need a full perimeter treatment below for the subs and a tenting up top.

This is one month into this purchase, and I am dealing with a new roof, two species of termites.  Fun fun fun.

Anyone redone a flat roof lately?  I am getting bids from roofing contractors and am debating between the traditional 2 ply asphalt (cap sheet, hot mod layers of modified felts or fiberglass), versus TPO, versus PVC, and also underneath them, a tapered insulation to give it a bit of pitch for water runoff.  Never seen a TPO or PVC roof, so I am not sure of their longevity and whether it is worth the extra $.

Sorry to hear about all of the unexpected capex! I can't help but feel your pain.

as a contractor a tpo roof is great if you can afford it

@Sam Leon  

Water dispersion is one of the characteristics of a Green Roof ;-)  It is quite possible the compost on your roof, and the matter growing in it, was masking the leaks.

Termites are something with which we thankfully do not have to deal up here ... yet {I hear they are in parts of Maine now, so it will just be a matter of time and a couple of mild winters before they find the tasty old Second Empire, Queen Anne, Victorian .... buffet which awaits.

1(506) 471-4126

@Jeremy Tillotson I am deciding between a traditional 2 ply system, versus TPO, versus PVC.   The 2 ply is cheapest and the PVC is the most expensive, with the TPO somewhere in between.

Then there are options to just redo the roof, versus put in a layer of flat insulation (which adds about $3000), versus put in a tapered ISO insulation to give the roof a bit of a pitch (which adds about $7000).  So with the three roofing membrane options and the insulation options, I am struggling to find the right balance.

@Roy N.   may be I should have built a curb around the flat roof and leave the compost and let it continue to build up, and just put weep holes around the perimeter for draining LOL.

I tend to buy older properties, wood studs and plates, plastered walls etc...so I tend to run into termites.  Right now I am looking at three sets of proposals for tenting three properties.  They are not giving me any discounts on signing three at the same time.  If yours are newer with metal studs there is less food for the termites to feast on.  On one house I have they left the trusses alone, but ate away all the 1X3 ceiling furring strips nailed to the bottom of the trusses, turned them into swiss cheese i can crunch with bare hands.  I was told the structural, harder, southern yellow pine are harder to attack then the softer furring, which is good.

@Sam Leon  If you plan to own this forever or to pass it to heirs then I would do the pitch with tpo. PVC is really great, but I never thought it to be worth the price difference. TPO properly installed should last for 30-50 years, if you have the slope. Most flat roofs end up with puddles and that is the problem.  IF you don't plan to own long you may be able to do a simple recoat that should buy you a few years, and would be MUCH cheaper, but if you plan to own do it right with the slope. 

Hey @Sam Leon sorry about your luck.  I had a roof here redone and went with the membrane sheeting but put the insulation boards underneath with a slight pitch.  That was about 20 years ago and it still looks great with no leaks.

@Sam Leon  

That's too bad about the termites.  I'm glad we don't have to deal with them in Minnesota.  As a roofing estimator I highly recommend PVC membrane.  They last FOREVER because the membrane is prefabricated and hand welded at the seams.  Seamless roofing= no way for water to penetrate through. Duro-Last is my favorite manufacturer.  TPO is great too. 

I would stay away from built-ups and EPDM.  You will be dealing with the same issue in 15 year or less and they are both a maintenance issue which adds to the cost.  Do it right the first time.   

Good luck!

As an experienced contractor, forget the 2 ply Built up Roof (BUR) that's a maintenance system at best.  Consider a torch applied APP modified bitumen instead.   To be code compliant the roof needs to be sloped a minimum of 1/4" per lf, with built in crickets to direct the rain water flow to the drainage locations, if required because of the roof configuration.

Now about tapering (building the slope) there are three basic methods:
1.  Carpenter approach, that is frame it and sheath it with plywood.

2.  Design a tapered insulation system using Expanded Poly Styrene EPS and use a recover type board over the top to separate the insulation from the torch applied membrane.

3.  Similar to 2 above, except using Poly Iso Cyanurate to gain a much higher R value, if that is an important consideration.  Poly Iso is available in stock panels to do this.

Roof venting is an important consideration, either into and out of an attic space or the joist cavities - you need both intake and exhaust.

Now about single ply roofs which come in various thicknesses, I'm considering 45mil products here which is the usual residential thickness sold - TPO is the cheapest but usually costs more than a torch applied APP.  PVC costs about 10% more in our market and the top of the line KEE (a modified PVC with woven and sealed reinforcement is 30% higher.  They all require high quality workmanship skills with TPO the most difficult to handle because of its stiffness.  Robotic welding is required on all seams exceeding 10lf by manufacture convention.  If the contractor doesn't have a robotic welder don't do business with them. 

More help is available in terms of advise if needed, just let me know.

Sorry to hear about termites, also sorry to hear that you have to do this work with tenants living there.  Since you obviously holding this long term, the best, cheapest route to go (in my opinion) is rubber.  Did you say how many ft^2 the roof area is?  Im from Pittsburgh, so we may need things that you do not in south Florida. 

Sounds like you need all new material (hopefully your joists are fine), I use 3/4" plywood standard or maybe tongue and groove OSB.  I put 1" isofoam (for insulation) and anchor it to wood (8"-16" on centers), Then the roofing adhesive (there is a lot of brands and cant remember what Ive used off the top of my head), but its expensive like $150-$200/5gal.  Act fast with it esp in hot Florida sun!  A standard 10X50 roll I pay like $275 for.  In my experience this is the fastest and cheapest way to go.  Im not a roofer, but I can lay rubber roofs on my rentals, and they're still holding.

I'd definitely go with the TPO or PVC.  I would never, ever do a build up.  About 5 years ago I was president of a congregation with two churches and two grade schools.  Two of the roofs were bad and really needed to be redone.  One of the others was a newer build up, but it had been 'maintained' and patched to deal with the leaks that had sprung.  This was a huge unexpected expense for us.  We got bids and I lobbied hard for the TPO.  We did one church and one school with the TPO with tapered insulation above as you described.  5 years later we've had no issues at all with either of the new roofs and the other build up roof has been continuous problems until last summer when it was also replaced with TPO.  The white membranes are durable, but if a problem would develop, you can find the whole and patch it.  With a build up roof, you've got a bunch of gravel over layers of asphalt.  Asphalt degrades over time fairly quickly.  The gravel is supposed to protect the asphalt, but that's not always how it works and when there is a problem, you're really out of luck.  How are you going to find it with all the gravel and layers of roofing?  Additionally, the white membranes significantly cut air conditioning costs in the summer. 

If you're going to hold long term go TPO/PVC.  If you're looking to save some money I've used GAF's Liberty self-adhering modified bitumen along with tapered foam insulation to give you some pitch.  I generally use that on porches or small additions that don't have the slope to do singles.  If it's your main roof then I'd really try to go TPO/PVC if it's in you budget.

This is why I don't buy any rentals with a flat main roof, that's one of my few hard limits....right up there with being too scared to get out of my truck during the day (which isn't often).  

Back in my commercial construction days, EPDM roofs were very popular due to their ease of installation, long service life, versatility and relatively inexpensive costs.  They can be installed for $2.50 to $3.00/sf depending on the area.  Of course, tapered insulation needs to be layered underneath to slope if there isn't currently one on the roof.  

A 'backwards jackpot', indeed.  I feel for you- I have always been leery of flat roofs, but out here it is because of occasional large snow loads, not compost loads!
If you had known about the roof you could have just offered rooftop garden plots as a tenant amenity....!

Fixed a flat rubber roof at a rental of mine a few months ago.  It just needed new plywood 16" along some of the edges and some plywood further in where there were soft spots.  Some of the rafters needed extra support as well along the edge and had to rebuild one of the walls because it was shot.  The rubber was in decent shape so I just installed a new drip edge and coated tar along the drip edge and new plywood and put rubber back down. 

Originally posted by @Peter MacKercher :

Did you get a building inspection? 

Yes.  But nowadays I do inspection just to sleep better.  Most times the inspector would not see as much as I do in my 30 minute initial tour since I know what to look for.

I knew the roof is old and near the end of it's life, I didn't expect cleaning debris off it would cause leaks.  Drywood termites I knew about - I mean I saw "evidence of", which is for the most part what a termite inspection would tell you, whether there is evidence of termites.  For a building that's 50 years old in Florida, there is always going to be evidence of termites.  They can never tell you whether there is actual live termites at the time of inspection.  Sometimes if they see wings they can tell you there were winged reproductives from the last swarmping season.  The subterranean termites was a big surprise to me.

Originally posted by @Shane Setzer :

@Sam Leon 

That's too bad about the termites.  I'm glad we don't have to deal with them in Minnesota.  As a roofing estimator I highly recommend PVC membrane.  They last FOREVER because the membrane is prefabricated and hand welded at the seams.  Seamless roofing= no way for water to penetrate through. Duro-Last is my favorite manufacturer.  TPO is great too. 

I would stay away from built-ups and EPDM.  You will be dealing with the same issue in 15 year or less and they are both a maintenance issue which adds to the cost.  Do it right the first time.   

Good luck!

The quotes I have been getting on TPO is made by GAF.  They are recommending the 60mil product to me.

What I have been told is the TPO being white reflective will have some energy saving quality.

What I can't decide is whether I need insulation below the TPO.  The roofing contractor says I don't.

Originally posted by @Sam Leon :
The quotes I have been getting on TPO is made by GAF.  They are recommending the 60mil product to me.

What I have been told is the TPO being white reflective will have some energy saving quality.

What I can't decide is whether I need insulation below the TPO.  The roofing contractor says I don't.

 What is the current R (RSi) factor of your roof /attic space?  If it is less than R40, adding more insulation would be a very good thing.   Whether you are trying to keep the heat in (most of the year up here) or out (most of the year in Florida), the better the thermal break of the envelope, the lower your energy costs.

1(506) 471-4126
Originally posted by @Dave Hill :

As an experienced contractor, forget the 2 ply Built up Roof (BUR) that's a maintenance system at best.  Consider a torch applied APP modified bitumen instead.   To be code compliant the roof needs to be sloped a minimum of 1/4" per lf, with built in crickets to direct the rain water flow to the drainage locations, if required because of the roof configuration.

Now about tapering (building the slope) there are three basic methods:
1.  Carpenter approach, that is frame it and sheath it with plywood.

2.  Design a tapered insulation system using Expanded Poly Styrene EPS and use a recover type board over the top to separate the insulation from the torch applied membrane.

3.  Similar to 2 above, except using Poly Iso Cyanurate to gain a much higher R value, if that is an important consideration.  Poly Iso is available in stock panels to do this.

Roof venting is an important consideration, either into and out of an attic space or the joist cavities - you need both intake and exhaust.

Now about single ply roofs which come in various thicknesses, I'm considering 45mil products here which is the usual residential thickness sold - TPO is the cheapest but usually costs more than a torch applied APP.  PVC costs about 10% more in our market and the top of the line KEE (a modified PVC with woven and sealed reinforcement is 30% higher.  They all require high quality workmanship skills with TPO the most difficult to handle because of its stiffness.  Robotic welding is required on all seams exceeding 10lf by manufacture convention.  If the contractor doesn't have a robotic welder don't do business with them. 

More help is available in terms of advise if needed, just let me know.

The roofing contractor does have a robot to heat weld the seams.

However, this single layer of TPO at 60mil thick sits directly on top of the T&G roof deck.  How is the TPO material itself adhered to the roof deck?  I believe mechanically fastened?  If so, how are the holes created by the mechanical fastening process sealed?  Is it also a heat welded "patch" done by robots?

My roof area is very simple, like a rectangle, not walls, no curbs, no valleys, just a simple flat roof about 2200 SF.  The quote I got for the TPO is about $8 per SF, close to $18000, this is just for the TPO, not including any roof deck repair, fascia repair, those are additional $6.50 per linear foot.  If I want a regular insulation under that, it's an added $4000, if I want a tapered iso insulation of 1/4" per foot under it, it's an added $8500.

The biggest questions I have about TPO is:

(1) How is it fastened to the roof and sealed off.

(2) I heard that TPO has a manufacturer's backed warranty.  However in searching online on TPO I saw many reviews saying TPO warranty is for commercial not for residential.

(3) Do I need insulation under TPO?

(4) If the roof deck is not perfect, let's say a slight depression due to imperfect framing of the roof structure, it will pond water.  Does it deal with ponded water or puddles well?

(5) How would one repair a TPO roof?  Let's say a crack or tear.  Do they patch a new piece of TPO over the existing damages, and heat weld that over?  Only TPO contractors can repair TPO roofs right?

@Sam Leon  

In MN, the state law requires the R Value to be 23 or higher.  Typically you don't have to bring the R Value up to code with a layover, but if you were to do a tear off (removing the roofing down to the decking) you would need to bring it up to code.  Chances are you have insulation in your attic.  It's never a bad idea to add insulation to your roof as it will only save you money in the long run.  Also, if your attic is insulated with fiberglass, it may have lost it's R-Value when it got wet.  If you trust your contractor, go with his decision, he's the professional.  Whatever you do, just trust your gut.

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