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Question DetailsAsked on 4/26/2013

I am looking for a rough estimate for a shed dormer with an approximate length of 10 feet (with windows) -- exterior finish only. Thank you!

The shed dormer will open up our attic and bring in more light. Our house is old -- built in the 1910s, so extra floor support may be needed. At this stage, we are looking to complete the exterior only (we are planning to renovate our attic in stages).

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4 Answers


Tough to answer without making a visit to the home mark.

What type of windows?


The structural work is the toughest.

Is it a 2 story home or a ranch?

All these questions affect the price.

Shingle or rubber roof? Depending on pitch.

What about existing roof, maybe you need a new roof on

Dormer side or both sides.

I live in Boston so prices vary depending on location.

If it were around here I would tell you to have a budget between

12 and $16,000.

Thats around here.

Answered 6 years ago by pats fan


The $10-20K estimate provided in the first response sounds like in the ballpark, depending primarily on how fancy you go, and especially on whether you leave in the existing roof joists and fit the windows in between them, or try to take them out, which means a significant roof structure modification.

Another thought - if you are primarily looking at more light and a bit of a more "open" look, have you considered between-joist skylight units ? These are designed to fit between the roof joists, and basically only require your roofer or window specialist cutting a hole in the roof, installing the unit with appropriate flashing and sealant, and you are done.

Type and cost depends on size, whether they are fixed or opening type, have blinds or not, energy efficiency, and whether their depth is only that of the roof framing system (4-8 inches), or if you are going to need a "light box" or "light tunnel", which is an opening leadingdown from the skylight to the finished opening interior wall/ceiling, to carry the light down from a recessed skylight.

The drop-in units come in both flat and dome-shaped configurations, and up to 4 feet in length do not get too expensive - a $200-600 for a 2 x 4 foot unit depending on energy efficiency and whether fixed or opening Bigger units get pretty pricey.

Installed cost for a non-opening drop-in by a roofer can run $800-2000, with additional $500-1000 per additional units on same job. Can run 50-100% more if you go with a double-width unit, as it requires removal of part of a roof joist, with associated structural modification to the roof framing.

One consideration is if you are in a deep snow area with winter-long snowpack on the roof, is putting in a "raised curb" under the unit (blocking-up of the roof surface before installing the skylight), both so the skylight is less often buried in snow, and to reduce the risk of ice damming and leakage from the snow melting around and on top of the window frame.

Also, as someone working in a high snowfall area, I would emphatically recommend doubled-up perimeter framing if you go with a double-wide unit (probably an extra $100-150), as cutting the hole for the unit removes a fair piece of the roof's snow load carrying capacity. Ditto in hurricane areas, but for wind uplift load instead.

Answered 6 years ago by LCD


Ya LCD some good ideas there.

I take from the question that head rooisomer so than light

Is the issue, I may be wrong.

Everything you described relating to the framing is

State code in this area.

He also mentioned the existing conditions of the joist

Which will now become the floor joists if he adds a dormer.

If they have to get beefed up it raises you floor height,

While also trying to save existing ceilings underneath.

All kinds of issues there.

Framing layout below.

Load bearing walls etc etc.

A rule of thumb mark for geting correct dimension of lumber

For a particular span is the following.

Measure the span of the room outside to outside,

Half that span and add 2.

Let's say it's 20' span.

20 divided by 2 = 10'.

10 + 2 = 12.

So it's a 2 by 12.

Always go up never down.

It may be confusing to measure in feet and convert to inches

But that's a quick way to size correct lumber.

Obviously there is engineered lumber etc.

Intermitent load bearing walls and framing layouts have a huge bearing on lumber sizes, dimensions etc, etc.

All the best with your project.

Answered 6 years ago by pats fan


I apolagise for the typos.

It should have said "headroom was more of an issue than light"

My apologies.

Answered 6 years ago by pats fan

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