"mountain953346" wrote:
> HI Strat..thanks for the great analysis and ideas you wrote..appreciate very much...I like all your options!> Question though on the the closed cell foam sheathing..
> Is it walkable on?
YES
> I wonder about the vertical strength if applied over the exisiting roof
That is "Deflection -limits"
> Wont it be pretty compressible? NO, you can walk on it and unless you weigh 1,000 lbs, your shoes won't leave an imprint.
Read More . . .
Two ways to answer you,
a simplified common sense approach, and the engineering approach which will involve lots of figures and math that's beyond the scope of this forum. But I'll include links to a couple of web resources for those who are inclined to read through the fine detailed analysis on their own.
If you are confident to walk on your current roof, then you'll be happy to know that after spraying top of your deck with 2 to 3" of "ccSPF", the overall deflection limit is going to be 1.5 to 3 times (depends on the thickness of foam) that of your current raw lumber deck.
If you want exact figures, research deflection-limit for your 1x8 wood roof, identify specie of wood, it'll take some work if you're interested). I couldn't find data on 1x8 planks as structural material because today's building codes don't allow anything less than OSB boards nailed to 2x4" studs.
Anyway, whatever you come up with for your 1x8 deck, multiply it by a factor of 1.5 to 3 and that's how much stronger your roof will be after sparying ccSPF.
Here are a couple of great pages to review:
- Benefits of ccSPF :
- SPF for in commercial buildings
- Refs: Deflection strength.
Hope this helps.
BTW. that first link is a real good resource because it covers ALL benefits of ccSPF, it covers vapor barrier, condensation, structural and insulation benefits.
-S-
>
> --- In DoIt_Yourself@yahoogroups.com, "Strat" wrote:
> >
>
> > (c)
> > Another option is applying another layer or two of rigid closed cell foam sheathing over existing roof, taping and staggering seams. This yields a very good result and very doable by DIY warriors.
> > This is my most desirable and cost effective option.
> >
> >
> > The other insulation materials like loose cellulose or fiberglass batting are not relevant to low pitch/flat roofs because there isn't adequate head-room to pack enough insulating material in to make an impact on R value.
> >
> > http://energy.gov/energysaver/articles/insulation-materials
> >
> > Good luck and we'll compare notes comes next Fall.
> > -S-
> >
> >
> >
> > --- In DoIt_Yourself@yahoogroups.com, "mountain953346" wrote:
> > >
> > > We have 2000 sq ft roof that is composed of 1x8's over
> > > 4x8 on 8ft centers, then asphalt roll and tar covering the 1x8's.
> > >
> > > That's it. There is no insulation and we are loosing most
> > > of AC and heat through the roof.(It is a low-slope "flat" roof)
> > >
> > > We have computed the costs for doing a new inside the house drywall
> > > ceiling dropped down 3 1/2" with r-15 fiberglass insulation
> > > at about $1.25 a sq ft. minus labor..having done drywall
> > > before we are confident to do the work although it seems
> > > a lot more intensive than adding new roof...??
> > >
> > > Add roof approach is to add 2x4s on 16in centers on the roof
> > > and put insulation there, then cover with 3/8" CDX and asphalt
> > > roll roofing over that which is now on the existing roof
> > > (maybe 25 year old roof now so could use a replacement)...
> > > essentially making a new roof....we also have done DIY
> > > in this area. Costs of materials about the same.
> > >
> > > It seems to me that the roof approach is way less labor
> > > intensive than beaming the inside ceiling, juggling
> > > even lightweight drywall, insulating and screwing and taping
> > > and mudding the inside ceiling...
> > >
> > > I would be very interested in the DIY'ers thoughts on the
> > > approaches to this project...or a new approach we have not
> > > thought of to solve this upward massive energy drain. In the
> > > summer the ceiling inside is a virtual radiator. We live
> > > in San Diego away from coast 15 miles so it gets hot but
> > > does cool off at night (semi-desert climate).
> > >
> > > Thanks in advance for any and all thoughts and ideas.
> > >
> > > Rich and Kate.
> >
>
> >
>
> > (c)
> > Another option is applying another layer or two of rigid closed cell foam sheathing over existing roof, taping and staggering seams. This yields a very good result and very doable by DIY warriors.
> > This is my most desirable and cost effective option.
> >
> >
> > The other insulation materials like loose cellulose or fiberglass batting are not relevant to low pitch/flat roofs because there isn't adequate head-room to pack enough insulating material in to make an impact on R value.
> >
> > http://energy.gov/energysaver/articles/insulation-materials
> >
> > Good luck and we'll compare notes comes next Fall.
> > -S-
> >
> >
> >
> > --- In DoIt_Yourself@yahoogroups.com, "mountain953346" wrote:
> > >
> > > We have 2000 sq ft roof that is composed of 1x8's over
> > > 4x8 on 8ft centers, then asphalt roll and tar covering the 1x8's.
> > >
> > > That's it. There is no insulation and we are loosing most
> > > of AC and heat through the roof.(It is a low-slope "flat" roof)
> > >
> > > We have computed the costs for doing a new inside the house drywall
> > > ceiling dropped down 3 1/2" with r-15 fiberglass insulation
> > > at about $1.25 a sq ft. minus labor..having done drywall
> > > before we are confident to do the work although it seems
> > > a lot more intensive than adding new roof...??
> > >
> > > Add roof approach is to add 2x4s on 16in centers on the roof
> > > and put insulation there, then cover with 3/8" CDX and asphalt
> > > roll roofing over that which is now on the existing roof
> > > (maybe 25 year old roof now so could use a replacement)...
> > > essentially making a new roof....we also have done DIY
> > > in this area. Costs of materials about the same.
> > >
> > > It seems to me that the roof approach is way less labor
> > > intensive than beaming the inside ceiling, juggling
> > > even lightweight drywall, insulating and screwing and taping
> > > and mudding the inside ceiling...
> > >
> > > I would be very interested in the DIY'ers thoughts on the
> > > approaches to this project...or a new approach we have not
> > > thought of to solve this upward massive energy drain. In the
> > > summer the ceiling inside is a virtual radiator. We live
> > > in San Diego away from coast 15 miles so it gets hot but
> > > does cool off at night (semi-desert climate).
> > >
> > > Thanks in advance for any and all thoughts and ideas.
> > >
> > > Rich and Kate.
> >
>
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