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ThePope 01-21-2012 01:09 AM

Converting attic to conditioned space
 
long time reader first time poster
i live in a very cold winter/rather hot climate of northwestern ontario, so insulation pays off and vapor barrier on the in-facing is the norm
my goal is to convert the attic of my 1940's bungalow into a conditioned space which will likely be used as a master bedroom with ensuite and an open rec area.
my house is 30x50 feet and the pitch of the roof allows over 10x50 feet of head room up there, but lots of space translates to lots of expense when looking at insulation prices.
i have looked at a few methods ranging from DIY sprayfoam which costs about $1.60/ board foot cdn for r7, to a mixture of sprayfoam and fiberglass, and fiberglass and foam board, and have come up with the following solution that is within my budget and DIY means

the roof rafters are 2x6's and run the 50foot length of my house, times 2.
my plan is to insulate approximately 9 feet of the rafters in the following method, and insulating the knee walls and new ceiling in a typical vapor barrier/r60 method

start by adding an additional 2x2 strapped on to the 2x6 rafters giving me an effective (5.5+1.75) 7.25 inches to work with.
add soffit vent channels between rafters from the knee walls to the ceiling (approx 9 foot span)
add r20 fiberglass batts (6inch) between the rafters, which should fit well in the 7.25inch space with the vent channels in there
add 2inches of foam board (r10) secured to the rafters with 1x2 ferring strips. taking care to tuck tape/sprayfoam any gaps in the foam as this will be my vapor barrier. my plan is to use extruded polstyrene that does not have any foil
drywall over that

big question is will this drywall hold? or will it be too easy to puch the screws through if you knock the wall too hard. ive seen videos of this method used in basement walls. perhaps i may go with tongue and groove pine boards as a finish if drywall wont work?

this method brings me to r30 for the angled part of the ceiling. for the knee walls and the new ceiling i will bring as close to r60 as possible. my soffits are well vented though i may add more, i have 3 vents near the ridge of my roof and the 2 gable vents

good enough? i estimate this whole job at around $4000 or so, whereas if i did straight sprayfoam i would be around $15000+

currently my insulation is pretty lacking. no vapor barrier and 3inches of sawdust and 3 inches of blown in loose fill. i have a pretty bad frost problem on the under siding of my roof, but this house has been like that for many years so ill be waiting till spring for this job

i hope i can contribute to other posters questions, however it may be 30 years of practice until im actually right

bob22 01-21-2012 08:50 AM

Leaving the insulation questions aside, will the ceiling joist system of the floor below (now your floor for the attic) support living space loads? I'd want to get that determined and fixed, if needed, first.

titanoman 01-21-2012 09:41 AM

Are you really the Pope?

titanoman 01-21-2012 09:48 AM

Quote:

Originally Posted by bob22
Leaving the insulation questions aside, will the ceiling joist system of the floor below (now your floor for the attic) support living space loads? I'd want to get that determined and fixed, if needed, first.

I don't think that's the question. Why "put his questions aside" when that's what he wants to know about?

bob22 01-21-2012 09:59 AM

Because if the floor needs to be strengthened and he/she determines they don't want to/can't do what is needed, then insulating is likely not needed any longer.
THere are also height requirements for habitable space and if raising the floor level to accommodate needed floor strengthening would now not make height requirements then insulating is off the table.

Ironlight 01-21-2012 10:04 AM

As you mention you're in an area where insulation pays off so I would expect that the performance of foam *might* pay for itself. I'm sure you ran the calculation to see if it would be worth it based on your energy costs and how long you expect to stay in the home. Can you share that with us? I'd just be curious to know what that looked like.

As for your proposed method, let me make sure I understand. The kneewalls will rise up to meet the joists, then those run up on each side approximately 4.5 feet to where they meet the new ceiling. The 1x2s would hold the foam board up how? Edged against the extended joists (so, against the 2x2s) running the length of the foam board edges, or horizontally, perpendicular to the joists? I assume the former so there is no air gap but I just want to make sure I understand.

If the former, you're concerned about the drywall and the screws along the portion that is affixed directly to the joists? The drywall will be screwed directly into the 2x2s, correct? The degree to which that is a problem is directly related to how much flex there is in your roof. The kneewalls and new ceiling will add some additional rigidity to your structure.

cibula11 01-21-2012 10:36 AM

when we were considering converting our attached garage to liveable space, we needed to provide R45 in the ceilings, even the vaulted part...which meant we had to build out or sister the current 2x6 to 2x12 in order to do so. You may want to figure out how much insulation is required for a vaulted ceiling, especially if permits are being pulled, which they probably should be.

It also sounds like sistering your joists and then using ONE product for insulation (batt or spray) would be simpler than your proposed method.

ThePope 01-21-2012 11:31 AM

the floor joists in the attic are 2x6's and run the 30 foot width of my house, supported by a continuous support wall at the 15 foot mark. i was planning on laminating another 2x6's to the current ones to give added strength without resulting in a loss of headroom.

i am not the pope, sorry.

as for the last question:
i did not do a cost benefit on the sprayfoam, i stopped when i saw it would be like $15,000 to do the attic. also its not as DIY friendly and contractors cost way too much where i live. i see its benefits of a solid vapor barrier @2-3 inches, a value of r7 per inch (according to manufacturer, but may be r6) which is higher than fiberglass batt ~r4 or foamboard ~r5. i live about 400 miles above Minneapolis but even in this harsh climate i cant afford sprayfoam. i see myself owning this house for a long time as it is 3 legal rental apartments but i may not live here as long (unless i convert attic in to living space)

ok, so to draw a better picture of the attic, the knee walls raise up about 5 feet from the soffits to meet the roof rafters at approximatley 2.5feet. my proposed method creates a fiberglass/foamboard angled wall that runs approx 9 feet to meet the new ceiling i will create that is then 8 feet tall. that ceiling will run approx 10 feet across to meet the other angled wall going down. this gives me a 10x50 foot area of 8 foot clearance, and on each side another 5 feet or so to each knee wall with the angled ceiling.

my plan is to extend the 2x6 rafters into 2x8 rafters by securing 2x2 strapping. the vent channels and fiberglass goes between it. directly over top of that i will put the foamboard secured in to the rafters, with furring strips running alongside each rafter every 16 inches. all seams would be tuck taped as this is my vapor barrier as well. i would then screw in the drywall with screws long enough to hit the furring strips and the 2x8 joists behind them (that would be 1/2inch for drywall, 1inch for firring strip, 2 inch to go through foam, and then some catch on the rafter so ~4.5inch screws)

as for pulling permits, i havent looked in to that :( we dont have the craziest codes here but since im converting this in to living space ill take a trip down to the city office and ask around

if i extended the rafters from 2x6 to 2x12 giving me 11 inches to put up fiberglass batts and vent channels i could fit r42 in the 11 inches with the vent channels and just vapor barrier over that, maybe ill look in to that aswell. any idea how to secure a 2x6 on end to another 2x6? just screw it in on an angle until it feels snug?

cibula11 01-21-2012 02:12 PM

Quote:

Originally Posted by ThePope (Post 829930)
the floor joists in the attic are 2x6's and run the 30 foot width of my house, supported by a continuous support wall at the 15 foot mark. i was planning on laminating another 2x6's to the current ones to give added strength without resulting in a loss of headroom.

i am not the pope, sorry.

as for the last question:
i did not do a cost benefit on the sprayfoam, i stopped when i saw it would be like $15,000 to do the attic. also its not as DIY friendly and contractors cost way too much where i live. i see its benefits of a solid vapor barrier @2-3 inches, a value of r7 per inch (according to manufacturer, but may be r6) which is higher than fiberglass batt ~r4 or foamboard ~r5. i live about 400 miles above Minneapolis but even in this harsh climate i cant afford sprayfoam. i see myself owning this house for a long time as it is 3 legal rental apartments but i may not live here as long (unless i convert attic in to living space)

ok, so to draw a better picture of the attic, the knee walls raise up about 5 feet from the soffits to meet the roof rafters at approximatley 2.5feet. my proposed method creates a fiberglass/foamboard angled wall that runs approx 9 feet to meet the new ceiling i will create that is then 8 feet tall. that ceiling will run approx 10 feet across to meet the other angled wall going down. this gives me a 10x50 foot area of 8 foot clearance, and on each side another 5 feet or so to each knee wall with the angled ceiling.

my plan is to extend the 2x6 rafters into 2x8 rafters by securing 2x2 strapping. the vent channels and fiberglass goes between it. directly over top of that i will put the foamboard secured in to the rafters, with furring strips running alongside each rafter every 16 inches. all seams would be tuck taped as this is my vapor barrier as well. i would then screw in the drywall with screws long enough to hit the furring strips and the 2x8 joists behind them (that would be 1/2inch for drywall, 1inch for firring strip, 2 inch to go through foam, and then some catch on the rafter so ~4.5inch screws)

as for pulling permits, i havent looked in to that :( we dont have the craziest codes here but since im converting this in to living space ill take a trip down to the city office and ask around

if i extended the rafters from 2x6 to 2x12 giving me 11 inches to put up fiberglass batts and vent channels i could fit r42 in the 11 inches with the vent channels and just vapor barrier over that, maybe ill look in to that aswell. any idea how to secure a 2x6 on end to another 2x6? just screw it in on an angle until it feels snug?




You wouldn't want to go end to end...rather sister a 2x12 along side the 2x6....if you just had to go a couple of inches out....you might be able to get away with going right on the end of the 2x6....but not to add another 6 inches.

BTW if the space is already considered liveable I don;t know if you need permits.

mae-ling 01-21-2012 02:23 PM

Quote:

Originally Posted by ThePope (Post 829930)
the floor joists in the attic are 2x6's and run the 30 foot width of my house, supported by a continuous support wall at the 15 foot mark. i was planning on laminating another 2x6's to the current ones to give added strength without resulting in a loss of headroom.

How far apart are they? 16" or 24" center to center.

Tried to find a span chart or calculator to do a double 2x6 and I could not. 15foot span for a double 2x6 on 16" centers sounds to small to me. If they are 24" apart then definitely.

Anyone have a span chart or calculator website for this?

ThePope 01-21-2012 02:59 PM

sorry i went back up there and had another look. they are 16 inch center to center and they are 2x8's. i confirmed that they are resting on the main support wall half way through the 30foot span, but have not checked if there are any more support walls (i do not believe so)

i also rechecked my head height with a little more light and patience. as it is now with 2x6 rafters, there is a span of only 80inches (6 2/3ft) that allows for 90 inches+ of headroom (7 1/2ft) and if im adding 2x6's and drywall that would cut down to 6 feet or so of headroom, and if i had to make 8 foot ceilings it would cut down further, and then factor losing a couple inches to subfloor and flooring. It seems so big up there still that i dont see why i cant get away with adding that space, even at 5 foot headroom span thats still 250sq ft with the additional side space

however as im looking deeper in to this project i am beginning to realize that my eyes may be deceiving me on the value of adding the attic space to my home without getting in to dormers/re pitching my roof

one major deciding factor is my ability to add a en-suite up there as well. my 2 stacks terminate through the roof behind the knee wall, but im getting in to a major reno.

AndyGump 01-21-2012 03:45 PM

When creating new living space like this it is advisable to get the project designed by a professional (Archy/Designer or Engineer).

That way all the various parts of the project will work together and ultimately cause you less problems.

The 2x8 in question @16" centers unless they are Doug Fir #1 will not fit the bill anyway. At least up to IRC 2009 standards.

Things like egress, insulation, natural lighting and venting and many other things need to be considered when taking on a project like this.

Andy.

Gary in WA 01-21-2012 04:18 PM

I agree, your floor joists would need to be doubled as well. Talk to the local AHJ, you may be required to double layer the drywall ceilings below in all the units for multiple dwelling fire safety....

Gary

ThePope 01-21-2012 08:17 PM

the more i look in to this the more it sounds like it isn't worth the grief. Although i would learn a lot in the process i may leave jobs like this to the professionals.

thanks for the help though.

however in the time ive spent thinking on this project i believe the mentioned method of strapping 2x6's on to the 2x6 rafters and filling with fiberglass batts (r40) would be the most economical method. as for the floor joists im sure the 2x8's 16 on center wouldnt do, so i would likely be doubling them up requiring 67 2x8x16feet at a cost of:
2x8x16 67 @ approx $11ea ~$740?
2x6x10 100 @ approx $5.40ea ~540?
r40 for angle walls ~$1000
r60 for knee walls and ceiling ~$500
drywall ~$1000 (blue stuff)
vapor barrier, tuck tape, screws, vent channels, etc ~$300

or
sprayfoam to r40 ~$15000

Gary in WA 01-21-2012 11:22 PM

Remember the new egress windows in each bedroom and upstairs, egress stairway to the converted space, new heat/light/ventilation required: http://docs.google.com/viewer?a=v&q=...1txlzU01V4JQIg

Gary


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