Are you sure they are not using live load joists already? I was under the impression that if they use attic trusses or show a bonus room that they would use floor joists already. The price is usually very economical.

If it is space that you plan to use in the near future I would suggest that you size the HVAC accordingly and plan the supply and return runs now. Also, I would consider running a future tube (capped 2" - 3" PVC pipe from the basement to the attic).

I would share our price with you but we are actually doing 1600 square feet of unfinished space attic space. We are roughing in the plumbing, doing HVAC runs, electrical and essentially everything except drywall and flooring (this will keep my tax base down until I am ready to use the space or get ready to sell the house.

We have an upstairs bonus room that we had originally planned to finish at a later date. We ended up getting it about 90% finished during our build. In retrospect, we could have eliminated the bonus room and saved a great deal of money and DIY time and labor but that's beside the point. One thing that I wish we would have done different is instead of running ductwork to that room, it would have been more economical to install a mini-split up there and just use it as needed instead of having it be part of the constant climate control of the entire house. Just a thought.

Most plans seem to list the bonus space separately, and you need to specify with your builder that it's to be liveable space.

No, we have NO plans to use this space any time in the near future. Maybe never. But I'm wondering whether the cost of the flooring and duct work would be worth flexibility in the future.

I had thought about something along the lines of a mini-split. It does seem to be logical.

If your roof will be made of trusses, I would upgrade to attic trusses to allow for 38" insulation. It will only cost ~few hundred $. As far as HVAC it wll need most likely 6" supply and 7" return to be cooled effectively. Flooring 2x4s and 2x6 are insufficient.

I would upgrade during framing. Not much money. It does not cost any different to install truss A vs truss B or frame floor with 2x10 vs 2x4s.

The one caution against doing it part way now to finish it "for the future", is that codes change... If you build it part way now under today's codes, you may not be able to finish it the way you thought when you get to "future". I'd either do it all, or not do it at all.

I agree that a space called a "bonus room" should contain floor joists sized to support a habitable space. If not, they should be changed or the name of the space changed in order to not mislead the buyer.

Thanks for the information, Casey.

Kirkhall, You bring up a valid concern, but I'm not going that direction. The house plan we've chosen has everything we need -- probably for the rest of our lives. Our ONLY reason for "prepping" the bonus space is that IF at some point our circumstances change, we want the space to be available. For example, if at some point one of our children moved back in with us, we might want to use that space. Or, if at some point in the future, our children inherit this house and think it would be perfect if only it had one more room, we'd want it to be ready to make into a real room.

Mind you, I'm not saying you're wrong about codes -- only that I think the possibility of us using this space is fairly remote, and I'm willing to chance it.

Ren8, I agree that this term is used -- perhaps purposefully? -- to confuse buyers. It sounds like, "Hey, here's a free room for you! A BONUS!" And it's easy to say, "Oh, look, we can afford to build an 1800 sf house! And it'll be comfortable for our family, especially with that big upstairs room!" And then once they realize the upstairs room is 500 sf OVER what they thought they could build, they've already bought the plans. Yeah, it's misleading.

Depending on the span, the additional structural strength for making a storage space into a habitable space is probably one joist size larger if there is any difference at all (20 psf becomes 30 pst). It should cost hundreds not thousands of dollars and would be very unwise to not do now.

If the bonus space is full of trusses then the builder is playing game with you.

If the plans say "optional bonus room" then you may be talking up to a few k more. If the plan says "future bonus room" or just "bonus room" the joists should already be calculated for live load or very reasonable to get there.

We have a space that was supposed to be inaccessible attic space, and the early drawings didn't have proper joists, just 2x6 supports for a ceiling below. I indicated that I wanted to put in an access door and use the space for storage. At that point, we had to add joists to properly support the floor and all the "stuff" above it. That added a couple hundred $.

And then, once it was built, and DH saw how much of our 3rd floor loft was real, usable space, he decided not to put up the wall closing off the storage space, and it's now part of the loft living area, and we're spending another couple thousand $ finishing it.

So even if you're thinking you'd only use it for storage, you'd probably need the joists to support yourself walking around up there.

these frogs (family room over garage) are notoriously
difficult to heat & cool.

google the term, bypass the pretty picture links
& read of the issues with these rooms.

foam insulating the walls & under the floor
area is the easiest way to address, other
than foam insulating the entire roofline, which is
the best option if locating ductwork in the attic space.

without additional air sealing & insulation it will
take a lot of a/c to heat cool these areas.
do a little proactive reading on them now.
then make an educated decision.

best of luck.