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Sunroom Additions, Three-Season and Four

The question that decides the budget is not size. It is whether the room is heated and cooled — and that answer changes the foundation, the glazing and the permit.

Get Your Fixed Price → ☎ (843) 718-8177

Sunlit dining addition lined with floor-to-ceiling windows and glass doors onto the patio, furnished with a trestle table and woven chairs

Licensed CLG.127339

Quick answer: A sunroom addition in the Charleston area typically runs $28,000 to $95,000. A three-season room costs substantially less than a conditioned four-season one. Southeastern Renovation is a licensed South Carolina general contractor (CLG.127339) serving Daniel Island, Mount Pleasant, Isle of Palms, Sullivan’s Island, James Island, West Ashley, Summerville and downtown Charleston. Every project is fixed-price in writing and backed by a 1-year workmanship warranty. Call (843) 718-8177 for an estimate.

200+ Renovations

Sunroom Addition

Sunroom Additions, Three-Season and Four

Sunrooms divide cleanly into two projects that happen to look alike. A three-season room is unconditioned: single glazing, no ductwork, and in Charleston it is genuinely comfortable perhaps eight months of the year. A four-season room is conditioned living space, which means insulation, HVAC, a code-compliant foundation and an energy-code review.

The four-season version costs roughly twice as much per square foot and adds to the heated square footage of the house, which matters at resale and on the tax assessment. Most of the disappointment we are called in to fix comes from someone buying the first and expecting the second.

Serving Charleston, Mount Pleasant, Daniel Island, Isle of Palms, Sullivan’s Island, West Ashley, James Island and Summerville — and the York County and Charlotte SC-metro side from Clover. Part of our Home Additions work.

Your Estimate in 3 Simple Steps

Decide conditioned or not

This one answer sets the foundation, the glazing, the permit path and roughly half the cost. We work through it before pricing.

Fixed price, in writing

Foundation, structure, glazing, electrical and any HVAC, priced and signed before work starts.

Four to eight weeks

Foundation, framing and roof, then glazing and finish. Permit, energy review and HOA submission handled.

Recent Sunroom Addition Projects

Mount Pleasant

Four-season room off the kitchen, mini-split, six weeks

James Island

Three-season room on an existing slab, four weeks

Summerville

Conditioned sunroom with a vaulted ceiling and clerestory glazing

Why Charleston Homeowners Choose Us

Straight answer on the tradeoff

We will tell you which version your budget actually buys before you fall in love with drawings for the other one.

Flood zone aware

Much of the Lowcountry sits in a mapped flood zone, and that dictates finished-floor elevation on an addition. We check before we design.

Built to carry the glass

Large glazed spans need a structure sized for them. Retrofit kits frequently are not.

Permit and HOA handled

Including energy-code review on conditioned space, which three-season kits do not require and four-season rooms do.

Common Questions

What does a sunroom cost in Charleston?

Roughly $28,000 to $95,000. A three-season room on an existing slab is at the low end. A conditioned four-season room with a new foundation, HVAC and energy-code compliance is at the high end and costs about twice per square foot what the three-season version does. Which one you are buying is the first thing to settle.

What is the difference between a three-season and four-season sunroom?

A three-season room is not heated or cooled and is not counted as living space. A four-season room is insulated, conditioned, built on a code-compliant foundation, and does count toward the heated square footage of the house — which affects appraisal, resale and property tax. In Charleston a three-season room is comfortable most of the year but genuinely unpleasant in July and August.

Does a sunroom add value to a Charleston home?

A conditioned four-season room adds heated square footage and appraises as living space. A three-season room generally does not, and is valued more like a screened porch or a deck. Neither typically returns its full cost at resale, so the honest reason to build one is that you want the room — the resale argument is secondary.

Can a sunroom be built in a flood zone?

Yes, but the finished floor elevation is dictated by the flood zone and the base flood elevation for your parcel, not by matching the existing house. On older Lowcountry homes the existing floor is sometimes below the current requirement, which means an addition cannot simply continue the same level. There is also a cumulative-improvement rule that can pull the whole structure into compliance. We check the parcel first.

Ready to talk about your sunroom addition?

Fixed price in writing · SC licensed CLG.127339 · Workers’ comp and liability on every jobsite

Get Your Fixed Price ☎ (843) 718-8177

Plan the cost around your scope and location

Decide whether the room is seasonal or conditioned. Compare foundation, glazing, insulation, heating or cooling, electrical work and the connection to the existing house as part of the same scope.

Browse cost guides by project and location

Published ranges are planning references for the scope and location named in each guide. Confirm your address, selections, allowances and exclusions in a written estimate. Fixed-price and cost-plus contracts are both available depending on scope.