Mudroom Addition on Cape Cod: What It Takes to Build One

A mudroom addition on Cape Cod is a small heated room built onto the driveway side of the house, on a foundation below frost, with a hard floor that shrugs off beach sand and wet boots, built-in cubbies and a bench, and its own exterior door. It is an addition, so it needs a building permit, and on a Route 6A lot it may need historic review first. Coast Carpentry Home Improvement builds mudroom additions on Cape Cod homes across Barnstable County, and this is how we plan one.

The room in the photo is the mudroom at our 84 Alden Drive new construction: white shiplap walls, a double door closet for coats and gear, and the white oak floor running straight through from the main hall. That house was drawn with its mudroom from the first sketch. On an existing Cape it is usually the room the house never had, and we add it as a bump out between the driveway and the kitchen. We are based at 14 Parker Rd, Unit A in Osterville, and Fagner Rodrigues, who holds the Massachusetts Construction Supervisor license that every Coast job runs under, draws the footing and roof plan on each one.

What is a mudroom addition, and why does a Cape Cod house need one?

Walk up to an older Cape in Yarmouth or Mashpee and the front door faces the street. Nobody uses it. The family comes in from the driveway, and on most of these houses that door opens straight into the kitchen. In August it brings in sand from the beach. In February it brings in snow, road salt and a wet dog. There is nowhere for any of it to stop.

The job of a mudroom is not storage. It is a place for wet things to stop before they reach the house. The floor can be mopped, the walls can be wiped, the boots have somewhere to drip and the coats have somewhere to hang that is not a kitchen chair. We get this call twice a year: in April, after a winter of boots piled by the kitchen door, and in September, after a summer of sweeping sand out of the kitchen.

Where should a mudroom addition go on a Cape Cod house?

On a Cape the driveway usually runs down one side of the house, so the mudroom goes on a side wall. That is the wall closest to the lot line, which is where zoning setbacks start to matter. A lot in Hyannis, South Yarmouth or Cotuit that was laid out before the current bylaw is often nonconforming already, and a bump out that lands inside the side setback needs a variance before it needs a footing. We measure the setback at the first visit, before anyone falls in love with a drawing.

The doors matter as much as the room. The exterior door should line up with the path from the car, the outdoor shower and the yard, with a storm door on it if that wall faces the prevailing wind. The door into the house should open into a hall or the kitchen, not the dining room. At 84 Alden Drive the mudroom opens into the main hall, so the sand stops two steps inside the door. Give it a window too. A mudroom with no daylight becomes a dumping ground.

What foundation does a mudroom addition need on Cape Cod sand?

Cape soil is outwash sand. It drains fast, which is good for a slab, and it slumps when it is disturbed, which is why we compact the base in lifts and set a wider footing than we would in clay. A slab is the natural choice for a mudroom. The floor is going to be tile and the room is going to be heated, so a slab lets us run electric radiant heat under the tile and the boots dry. The foam under and around the slab is what makes it a frost protected foundation, and that only works because the room is heated. An unheated room on a shallow slab will heave.

The frost wall wins when the house floor sits high off grade. Older Capes with a full basement have a first floor two or three steps above the driveway, and a slab at grade would leave a step down into the mudroom. We do not build mudrooms with a step at the inside door. That is the door people come through with groceries in both arms and a dog on a leash. So on a high house we pour a frost wall, frame an insulated floor over a crawlspace and set the mudroom floor level with the kitchen. What a mudroom never goes on is a deck frame or cantilevered joists. A cantilevered bump out is fine for a window seat, not for a room with a slab, a tile floor and an exterior door, and the addition types guide covers why.

How does a mudroom roof tie into the existing house?

The eave on a one and a half story Cape is low, so a shed roof off the side wall ends up with a shallow pitch. Shingles on a shallow pitch need the membrane under the whole roof, not just the eave, and we pitch the shed as steep as the eave height allows. The main roof above it dumps snow and meltwater onto that low roof all winter, which is exactly how an ice dam starts. Our ice dam guide explains the mechanics. The short version is a continuous membrane, a well insulated ceiling, and a gutter at the shed eave so the drip line lands away from the new door.

The wall flashing is the other place a mudroom leaks. Where the shed roof meets the house we cut the existing siding back, set step flashing under each course of shingles, and finish with a kick out flashing at the bottom so water leaves the wall instead of running behind the siding. On a cedar house the new wall gets Grade A white cedar shingles to match, and they weather in to the same gray over a couple of seasons.

Which floor holds up to beach sand and wet boots?

Beach sand is grit. Walk it across a wood finish every day for a summer and the finish goes dull in a path from the door to the kitchen. Tile does not care. The two things we watch on tile are the surface and the grout. A polished tile is a skating rink when it is wet, so we spec a textured or matte porcelain. Grout gets a darker color and a sealer, because white grout in a mudroom is gray by the Fourth of July. Slate is a good coastal floor in an older house, but it is natural stone and needs sealing on a schedule.

The Alden Drive mudroom runs the white oak through from the hall, so the house reads as one floor from the front door to the mudroom door. That is a real choice with a real trade off: the floor looks better, and the boot zone at the exterior door gets a tray and a mat because the finish there will see wear first. On a house with kids, dogs and a boat, we steer to tile. Walls take as much abuse as the floor, so shiplap or beadboard wainscot to bench height in a scrubbable paint, as at Alden Drive, is what we build on most of ours.

What built-ins belong in a Cape Cod mudroom?

The built-ins are what make it a mudroom instead of a hallway, and they are finish carpentry on Cape Cod, the same work as a kitchen island or a built-in bookcase. We draw them to the people in the house. Hooks go at adult height and at kid height. Cubbies get one per person, open, because a closed cubby with a wet boot in it smells by Tuesday. The bench is deep enough to sit on and sturdy enough to stand on, since someone will. One tall closet, like the double door closet at Alden Drive, takes the long coats, the beach umbrella and the vacuum. Our interior trim guide covers how we build paint grade work so it survives being kicked.

Two additions people ask for change the permit set. A laundry in the mudroom keeps sandy towels out of the house, and a dog wash station is close behind. Both bring water and a drain into the room, which means a plumbing permit and a vent, and both push the room from a slab toward a frost wall with a crawlspace the pipes can run through. Neither changes your septic design flow. The plumbing side of the cost works the same way we lay out in our bathroom addition cost guide.

What permits does a mudroom addition need on Cape Cod?

Every mudroom addition changes the footprint and the roof, so it needs a building permit, pulled under a Construction Supervisor license. In the Town of Barnstable the application goes to the Building Division, and each of the other Cape towns has its own. Zoning comes first: the building department checks the side setback and the lot coverage before it looks at the framing plan, and on a nonconforming lot that can send the project to the zoning board for a variance. We would rather find that out at the setback stake than at the counter.

Within 100 feet of a wetland, a pond, a marsh or a coastal bank, the Conservation Commission issues an Order of Conditions before the building permit is released, and a surprising number of Cape lots are inside that line. North of Route 6 from Sandwich through Orleans, the Old King’s Highway Regional Historic District Committee reviews any change visible from a public way, and a mudroom on the driveway side of a 6A antique usually is. On a lot in a mapped flood zone the addition has to meet the flood construction rules, which can change the foundation.

Title 5, the state septic code, sizes a system by bedrooms. A mudroom is not a bedroom, so it does not change the design flow or trigger a system upgrade. The Board of Health reads the plan when the permit is filed, so we label the room, draw the bench and the cubbies on the plan and keep the exterior door in it. Nobody can read a room like that as a bedroom.

What drives the cost of a mudroom addition on Cape Cod?

We do not publish mudroom prices, because two mudrooms of the same size can be very different jobs. A slab at grade off a kitchen door on a flat lot is the simple end. A frost wall with a crawlspace under a high first floor, a laundry in the room, a gable roof on a gable end wall and historic review on 6A is the other end, and the two rooms can look the same from inside. The built-ins move the number more than people expect, because a wall of fitted cubbies, a bench and a closet is a full week of finish carpentry.

What we can tell you is which end your house is on, usually in one visit. Send us the house through our quote request, we will walk the driveway side with you, and the written quote will list the foundation, the roof, the floor, the carpentry and the plumbing as separate lines. Our home additions process guide explains how we run the job from that first visit to the final inspection.

When is a mudroom addition the wrong move?

Plenty of Capes already have the room. A breezeway between the house and the garage is a mudroom with no walls, and closing it in is a smaller job than an addition because the roof and the slab are already there. A garage with a door into the kitchen can give up a corner for a bench and cubbies. A back hall can be fitted out with built-ins in a week. If the house has any of these, we will tell you to use it before we draw a new foundation.

The other case is the house that is about to need more than a mudroom. If the owners are also talking about a bedroom or a bigger kitchen, a mudroom bolted on now can end up in the way of the shed dormer or the sunroom that comes next, and it is cheaper to plan them together. And if the roof is at the end of its life and the windows are single pane, the mudroom waits. We build the shell right first, then the rooms off it. Our home additions on Cape Cod page shows the additions we build so you can see where a mudroom fits in the larger plan.

Frequently asked questions about mudroom additions on Cape Cod