Many people, when thinking of improving a building, have a vague idea that it is deficient, and want to improve it, but don't realize the work involved, or the ultimate cost. In a lot of these cases, I see owners wanting a great finished workspace, but they are very resistant to what the real cost is to get that. They want to throw up a little insulation and some sheet-rock, and boom, it's done. But looking at improving a building like this, and using it for higher purposes than it was originally designed for, requires a more overall approach.
The first thing that you must do, is decide what uses you want to make of the space.
Then you need to make a complete inspection to determine the existing conditions.
From this, you can then start to make a list of improvements that will take you to your goal.
One thing I didn't get to ask about this structure is, what are the existing shingles? 1 or 2 layers? Are they near to needing replacement?
And the slab and foundation, what are their condition? Is water drainage a problem? Are sills rotting out? What about the exterior siding? Most of these garages were built with painted horizontal wood siding. Paint is usually flaking. Wood is usually rotting in places. No house wrap. No insulation. No metal connections between wall and roof. Usually there is little or no roof overhang. Many times no eave or roof venting. I am surrounded by these exact kinds of garages. They are designed to simply cover and protect and enclose cars, from the weather.
Hip roofs have additional problems because of the difficulty they present structurally. They are not designed for any additional loads, as would be imposed by insulating and finishing the inside. Frankly, if it were mine, and ready for re-shingling, I would re-frame it into a gable end roof. This would be especially true if wanting to insulate and finish at the rafters. If you don't use the space above the ceiling for storage, then you can place adequate insulation there, and the whole venting problem disappears.
I notice that the roof deck is boards, which are heavier than OSB. These are all things to take into consideration when contemplating improvements.
The other thing in these cases, is the resistance of the owner, to hiring work. Everyone wants to just do it themselves, to save money. In a case like this one, it may be just better cost wise, to have the rafter spaces foamed professionally. It solves the venting problems. Even when properly vented, there is just not enough depth in a 2x6 rafter to adequately insulate. And if you add rigid insulation board, then how do you finish it? If you then ad sheet rock or drywall, then you have weight problems to consider. And the cost has now probably exceeded foam now, too.
Let's discuss your options step by step, again.
If you simply insulate at the rafters and don't hang drywall, then you don't need a full set of ceiling joists, designed to support storage. But I would make sure I still had a few ceiling joists, especially in the middle of the structure, that were fastened to the outside walls securely, so they would resist outward pressure from the rafters. But if you are going to do this, why not size and space them so you can use the space for storage? If you do this, then you can also finish their underside with drywall for a nice ceiling and hang lighting. To get access to this storage, I recommend a large hatch be framed at one or both ends.
If money is short, simply install a few ceiling joists in the middle of the structure for now, for bracing. But size them for the future storage ceiling. Then insulate your rafters.
I discussed the insulation of a hip roof in a prior post. Read it. It gives you your options.
Here's my checklist for garage structures of this type.
Check roofing material type, number of layers and condition.
Check decking material and condition.
Check for roof overhang and venting at eave and peak or gable ends.
Check for damaged fascia and water damage to exterior walls from roof leaks at wall junction/fascia/gutter detail.
Note exterior siding type and condition and look for water damage to siding and structure from inadequate sealing between board siding and failing paint.
Check sill plates and look for damage from improper surrounding grade and/or level of slab being too low.
Check condition of slab and footings or foundations.
Examine garage door header for inadequate design and excessive deflection.
Check design of roof framing and note capacity for additional loads from finishing space. Also look for evidence of exterior walls bowing out and roof-line developing swayback from inadequate bracing from wall to wall. Check ridge board for splitting and failure.
Check garage door for insulating value and gasketing and sealing.
Check windows for insulating value.
Check all openings for security methods implemented.
Examine electrical service and determine future needs for power and light.
Check if other utilities are available and determine if needed.
These are all areas in which these type of structures are inadequate and I have seen failures. In my neighborhood there are these exact same garages with bowed out side walls, sway backed roofs, rotted out exterior wall framing, rotting siding, deteriorating sill plates, tilting structures, failed and collapsed roofs, cracked and tilting slabs etc.
And I forgot to talk about footings and foundations and grading and excavation and compacted fill and setting the finish floor elevation.
Also, attention should be given to shear walls on either side of garage door openings. A neighbors garage is tilting and will collapse because of a combination of inadequate foundation, cracking and shifting slab parts and no shear wall protection for small walls on either side of the door.
Not to mention heating and cooling and de-humidification.
There are a lot of improvements needed to make some of these structures useful as finished workspaces.
Bill
