ADDING A BUMPOUT: A More Spacious Look For Relatively Small Bucks

Sometimes a bay window is enough to give a room
 the illusion of more space. This is one of the
cheapest and simplest kinds of bumpout.

People often ask me how they can add just a few feet of space to small bedrooms and the like without spending the inheritance. Alas, adding on small areas usually isn’t cost effective, since enclosing a small volume costs more than enclosing a lot. In certain cases, however, there’s a simple way to do it:  It’s called a “popout” or “bumpout”.

A bumpout is really just an overgrown bay window that extends the full width of a room or nearly so. It’s less expensive than an ordinary addition because it’s tucked beneath the existing roof overhang. By sparing the high cost of roof modifications, a simple bumpout can often be built for less than $10,000.  

Cramped bedrooms are the simplest and most common candidates for a bumpout. Tight kitchens or breakfast rooms can also benefit, but beware: Adding a bumpout in these locations will probably cost more because of the additional plumbing and wiring that must be rerouted.

This bumpout probably doesn't
encroach on the building setback,
since it doesn't project any further
than the existing house.
But as for you, check your zoning.

Before you consider adding a bumpout, check your local zoning laws and make sure it won’t be encroaching on the “setback”, the area of your property you’re not allowed to build on. While the roof overhang is generally allowed to project into the setback, the rest of the house isn’t, so don’t assume that a projecting roof gives you carte blanche to add on beneath it.  

If your zoning checks out, and if you have a reasonably broad roof overhang, you may be able to push the room’s wall out and capture two or more feet of extra space beneath the eaves. Although the new wall can be bumped out all the way to the back side of the gutter or fascia, it’s better to leave a few inches of overhang to preserve a small shadowline.  It’ll also reduce the likelihood of leaks.

In some instances, you may not even need a new foundation beneath your bumpout.  If the floor joists in the room you want to expand run perpendicular to the outside wall, and if there’ll be at least 18” of clearance to the ground beneath them, you may be able to “sister” new joists onto the existing ones in order to cantilever the bumpout beyond the foundation wall.  

Top-quality materials make for a
beautifully-integrated bumpout.
The foundation, however, makes
for a very expensive one.

If the joists run parallel to the outside wall, or if there’s less than 18” clearance to the ground outside, you’ll probably need a conventional foundation beneath the bumpout. That means appreciable extra cost, so ask an architect or contractor if this route will be worthwhile.

Since the bumpout will usually be very conspicuous from outside, it should be carefully integrated into your home’s architecture. The exterior finish is especially important. Either repeat your home's existing finish on the bumpout, or use a high-quality accent material such as wood siding, shingle, or whatever best suits the style of your home. Don’t just slap some bargain-basement plywood; it’ll look tacked-on and will hurt your home’s resale value. Go rattle your architect’s cage if you need design help.

 Whoah—these wimpy brackets don't
look visually strong enough to
support this bumpout.
Think, man, think!

 
On the interior, the floor material should extend from the existing room into the bumpout without any obvious change in floor level.  The ceiling will have to be lower inside the bumped-out area because of the roof’s slope, and because a beam will usually be required to support the roof where the wall has been removed. If the room you're expanding has a flat ceiling, it’s generally best to soffit or “box in” the bumpout ceiling rather than following the sloping underside of the roof.  The soffit can also contain recessed lighting if appropriate.

Finally, because of structural reasons, the bumpout will cost less if it’s slightly narrower than the room, rather than full width.  Combined with the dropped ceiling, it may also look better—it’ll give more of an alcove effect.