Solar on 2x4 Roof Trusses

KoolKev

Is it feasible to put solar on a shingle roof with 2x4 trusses without beefing them up/consulting an engineer? 1954 house one layer of shingles. Appears to be original sheathing not plywood. Roof in good condition so replacing doesn't seem justified. Inglewood California  so no snow load and 85mph 3 second wind load. I was hoping for a 5kw system but 2-3kw would cover my usage now with gas water heater and furnace.

mike95490

I'm no mech engineer.  Depends on the spacing and span, and how much termite damage.  I think you have to get a consult, or show that the space & span meets current requirements.

BB.

I have an 80 year old home with rough 2x4 that, with permits, has a 3.3 kW array.

It had not blown off, but I would not do it of my home was on a windy bluff/subjected to direct wind (hurricane, full on to coastal wind storms. Those through beam bolts take a lot of wood away.

If a structural engineer signs off, your insurance should be good.

If your roof is over 15 years old, get a new roof first.

If asphalt shingle, after 20 years, they can leak (no matter the 40+ year warrantee).

My two cents worth of opinion.

-Bill

vtmaps

KoolKev said:

Roof in good condition so replacing doesn't seem justified.

I generally don't like to fix what isn't broken, but the solar panels may function well for decades.  They will probably outlast your current roof.  Replace the roof before you put up your panels.

--vtMaps

KoolKev

Due to cost, I would only replace the roof if I have to replace the sheathing. It has quite a lot of life in it.
The 2x4's are on 24" spacing.

Does beefing require an engineer or can I follow some pre-planned direction like sister with 2x6 and/or add a perlin to cut the span and transfer the load.

BB.

My building department required a licensed engineer to sign off.

-Bill

MarkC

My metal building (24'x14' with metal roof) was constructed with 24" spaced 2x4 (dimensional).  My major concern was walking safely on the roof during the addition of the PV system.   I added another 2x4 (with short 2x4 spacers) side by side to the original 2x4s.  Also added cross rafters of 2x6 s - that you already undoubtedly have.  Then added additional triangulation supports mid-beam from these rafters.  I used torque type wood screws thru the "spacers" at all connections.  I also tied the bottom of all studs to the floor plate with metal straps (hurricanes here).    The benefits of this design is that "twisting" of the roof rafters is substantially reduced, it is relatively easy (usually very little interference) and is cost effective.  An unexpected advantage for me was I now have an "attic" space that is separated by 1/2" insulated panels mounted below the rafters.  The hot air above these panels is drawn out by a ventilator, substantially reducing the inside temperature.

You can do a "reasonableness" check;
http://www.awc.org/codes-standards/calculators-software/spancalc

Skippy

My advice :

Don't do anything on your own.
Meaning . . . go ask someone in charge.... building inspector . .  local hydro company . .  ect . .
It may mean just sistering a few 2x6's or it may mean a whole new roof . . you won't know till you ask.

I built my shed .  . drew up the plans, picked up the building permit and told the inspector that I was putting solar on the roof . . .
Mounted my 2 kw array on the roof and THEN had the building inspector in too have a look.
Not good.
First off, he would sign off on the building, BUT would not sign off on the panels . .  which were on the roof. . . so he would not sign off on the shed at all . .  until I had it engineered to specs . .  and since it was already built, it was a P.I.T.A.  (as in pain in the . .  ) to bring up too the engineers specs . .

2x4 on 24 inch centers only hold the roof up.  Wanna prove me wrong . . . get an engineer.

I would hate too see something happen (like a severe wind storm) and have your house collapse or get a severe lean . . . and then have you call the insurance just too find out . . .  too bad . . so sad . . If you get approval for the install and something happens, its still an act of God . . not your fault.

Just my opinion . .  or as I like to say . . . been there - done that - got the bill.

KoolKev

What would an engineer charge for something like this?

KoolKev

Skippy said:

"I built my shed .  . drew up the plans, picked up the building permit and told the inspector that I was putting solar on the roof . . .
Mounted my 2 kw array on the roof and THEN had the building inspector in too have a look."

Skippy, The plans were after the fact? Did the permitted plans include the solar system? If you submitted plans with solar system what was the particular gripe?

Skippy

I have a tendency to be a bit vague in my written correspondence  . .  . . sorry . . .

I built my shed . . .

then

Drew up the plans, picked up the permit, and told the inspector I was putting solar on the roof . . .

The permit was for the shed, not the solar . .  added the solar after the fact, with verbal notice to the inspector . .  when he arrived to do the final inspection, he was a bit surprised at the size and scope of the array . . . since it nearly covers the entire roof area of the shed (14 x 16)
Since the roof is 2x6 lumber on 18 inch centers, it can handle the loading . .. add to that , that the solar racking is transferring the panel loading to the outer walls, the building inspector agreed that there should be no problem . . .  just would not sign off on it until   it was engineered . . .

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As for engineering the 2x4 roof, I have no idea how much it would cost to get a guy in there . . .  there are alot of variables to that one . . .

I would go talk to at least three people, get a quote from each, and go from there.  You just need someone to o.k. it for the insurance to accept it.
Like my building inspector told me . . . the guy I have charges a bit more, but he is putting his business on the line.  something goes wrong, and I did what he told me to do . . . it's his butt on the line.

KoolKev

Kind of thinking of drawing up the plan to include the panels then taking it to the city planning for approval before I order anything. If I need an engineered solution I hope they let me know before approving the permit.