Buying a house with detached buildings is a great opportunity for additional storage, work, rental or living areas. Detached buildings can be offices, garages, barns, tiny homes, studios, mother-in-law cabins, short-term or long-term rentals, tool sheds, garden sheds, sound studios, and just about anything else. Well-maintained detached buildings can add utility and value and with proper repairs and maintenance can last as long as the main home.
In this article we will discuss ideas that can help people buy, sell or maintain detached buildings with greater confidence. We discuss the number one killer of detached buildings in the Foundation section, and other most common defects that we see as home inspectors (Foundation, Gutter System, and utilities such as Electrical Service and Septic/Sewer). Aside from common defects we also discuss best practice installations, maintenance items and some smart repair ideas.
Inspecting Detached building foundations
The number 1 destroyer of detached buildings is the same element that destroys all buildings: Water. Typically the damage starts from the ground and works its way up (not from the roof down like most people believe). With detached buildings, however, water’s destruction is rapid and total and can usually be observed within a decade or two.
Common foundation defects:
- Grade too high (grade near or at siding/framing)
- Grade sloped toward foundation areas
- Wood framing too close to the ground
- Shallow or missing footings
- Decayed floor framing
- No access to floor framing
- Poor grading and drainage
- High moisture at slabs and foundation walls
- Settling foundations– cracks and leaning/settling
- Wood Destroying Insect Damage
- Wood Destroying Fungus and Decay
- High moisture environments
Detached buildings with Wood Floor framing:
Best New Construction Practices for Detached buildings on a wood foundation :
There should be a minimum of 2′ clearance between the grade and the bottom of the floor framing– this clearance prevents pre-mature decay and allows a ‘crawl’ area for maintenance, inspections and repairs. Most of the issues above can be eliminated with a structure that was built higher off the ground. Posts should be installed over concrete footings– ideally the concrete footings extend below the frost line and at least 8″ above grade. Grading and drainage should be directed away from the building and especially away from the post footing areas to prevent settling. The building should have a gutter system with downspouts and extensions that direct water away from the foundation areas. Ideally the structure has at least 1′ roof overhangs to help protect the siding/trim from water damage. Wood siding/trim should be painted every 8 years or as needed. Wood structures should be treated for wood destroying insects as needed. Ideally a dehumidifier or AC system is used to control the interior humidity in the warmer/rainier periods to prevent mildew, mold and corrosion.
The #1 killer of Detached buildings on wood foundation systems
The condition that deteriorates detached buildings on posts, skids or blocks more than any other: when wood framing is installed on or near the ground. When the floor/wall framing of detached buildings is installed near the ground over time mulch, sediment and other organic debris mounds up against the siding and framing of the structure and the moisture starts a process of decay, wood destroying insects infestations and air quality issues which will eventually cause the structure to be worthless.
The best repairs for Detached buildings on wood foundation systems
Most smaller detached buildings on skids, blocks or posts can easily be raised or moved with beams, car jacks, and trailers. In some cases the grade can be excavated around the perimeter to improve the clearance and access. A minimum of 2′ clearance between the lowest point of the framing and the ground will allow good maintenance access under the building and prevent water damage over the long-term. Poured concrete footings should extend below the frost line and at least 8″ above grade (ideally more)— the recommended frost line depth varies based on region. Installing a detached building higher off the ground will require a ramp or steps to the door however the extra expense and trouble will yield life-long dividends by preserving the structure.
If the building cannot be moved or raised the surrounding grade should be repaired to direct water away from the building on all sides. A gutter system should be installed that directs water away from the foundation areas. Even when the framing is too close to the ground, grading and drainage repairs can at least extend the life expectancy of the structure.
Detached Buildings with Masonry walls or slabs:
Best New Construction Practices for Detached buildings on Masonry walls or slabs :
At or below grade detached buildings typically have masonry foundation walls and slabs which is why it is important that the surrounding grade slopes away from the home at all directions. The building should have a gutter system with downspouts and extensions that direct water away from the foundation areas– disconnected/leaking/damaged downspouts and missing/damaged/inadequate extension drains will cause structural issues over the long-term. Ideally the structure has at least 1′ roof overhangs to help protect the siding/trim from water damage. Wood siding/trim should be painted every 8 years or as needed. Wood structures should be treated for wood destroying insects as needed. Ideally a dehumidifier or AC system is used to control the interior humidity in the warmer/rainier periods to prevent mildew, mold and corrosion.
The #1 killer of Detached buildings on masonry walls or slabs
The condition that deteriorates detached buildings with masonry foundations more than any other: When the grade does not adequately slope away from the building. Run-off from the surrounding area and roof drainage will make its way toward the slab or foundation walls and cause cracks and deterioration and will eventually cause the structure to be worthless.
The Best Repairs for Detached buildings on masonry walls or slabs
The grade should slope away from the building at all sides (ideally a minimum of 6′ from the foundation areas). A gutter system should be installed and well maintained- run-off should be directed downhill and at least 6′ away from the foundation areas. Cracks in slabs or foundation walls should be sealed and monitored and mortar should be repaired as needed.
Many pre-manufactured storage buildings and detached structures have minimal overhangs which is unfortunate because a good overhang will protect the siding and trim over the long-term. Most storage buildings do not have a gutter system. A properly installed and maintained gutter system will help extend the life expectancy of the siding/trim and foundation areas of the detached building over the long-term.
Best practice gutter system installation and maintenance:
- Seamless gutters with downspouts and extension drains
- Gutters should be installed with adequate slope toward downspouts
- Drip edge flashing (should never be covered by the gutters)
- Gutter system drainage should exit downhill and at least 8′ away from foundation area
- Gutters should be regularly cleaned and maintained
- Gutters seams and corner should be re-sealed every 3 years or as needed
Common gutter system defects:
- Missing gutters
- Missing drip edge flashing
- Improperly installed or maintained gutters
- Loose, damaged, leaking, dis-connected or misaligned downspouts
- Missing, damaged, inadequate sub-surface drains
Electrical service improves the utility of an detached building and provides power for dehumidification or cooling which helps control moisture and extend the life expectancy of the structure. The service, or Amp capacity, and overall quality of installation may vary greatly– detached buildings may have no power, an extension cord run from the house, or a professionally installed 100 amp panel or larger, and everything in between. When buying a house with detached buildings the buyer should consider Amp rating of the sub-panels and overall construction quality. A good inspector can help anticipate repair/upgrade costs.
A note on the Ampacity or ‘Amp’ rating
Ampacity refers to the maximum load a system can safely handle. The ampacity of a sub-panel is typically limited by the thickness of the wires, the rating of the panel, and the distance of the service wires. These calculations are best performed by a licensed electrician.
Typical Amp Requirements:
Modern homes — 200 amp
Townhomes/Condos/ Smaller homes — 150 amp
Older Single Family Homes from the 60s/70s — 100 amp
Older Single Family Homes 50s/60s — 60 amp
Larger RV – 50 amp
Smaller RV – 30 amp
Dryer/Range – 30 amp
Typical extension cord or smaller electrical circuit for home (8 typical outlets) – 15 amp
Inspecting Detached Building Electrical systems:
Best Practice Electrical Installations:
- Minimum of 60 amp service
- Breakers, panel and wiring should be properly sized and rated
- Modern sub-panels require a 4 wire cable — 2 hots, 1 neutral, and 1 ground (rather than 3 wires)
- Neutral and ground wires should be isolated or not connected to the same bus bar or panel
- Conduit, or protective tubes, should be used to protect the service wire from damage (below panels and underground).
Common Electrical defects:
- 3 wire service only– recommend driven rod at the detached building for grounding
- Missing GFCI outlets – generally an easy fix
- Neutrals and grounds not isolated – generally an easy fix
- Breakers not compatible with panel – generally an easy fix
- Corroded panel due to high humidity – this is unsafe and the panel and breakers should be replaced
- Missing conduits – selective repairs or a full upgrade may be needed
- Service line not buried deep enough to prevent possible damage – full upgrade/replacement will be needed
- Under-sized service wires – full upgrade/replacement will be needed
- Missing sub-panel – full upgrade/replacement may be needed
Inspecting Detached Building Septic/Sewer Systems
Most detached buildings don’t have any plumbing. Some detached buildings will have a utility sink and others will have similar plumbing to small houses.
Best Practice Plumbing Installation:
- Permitted and professionally installed
- Water service line should be buried below the frost line with 14 gauge trace wire to help with location
- 3″ or 4″ Schedule 40 PVC waste lines with adequate slope to septic/sewer
- Main plumbing vent that exits through the roof
- Proper traps/vents/air admittance valves at all plumbing fixtures
- Main shut-off valve and shut-offs for each plumbing fixture
Common Plumbing Defects:
- Un-permitted — check with city/county planning
- Hose type water service (non-permanent) – full replacement needed
- Water service line that is not buried below the frost line and subject to freezing/bursting – full replacement needed
- Inadequate heat source to prevent plumbing from freezing – HVAC installation needed
- Waste line exits to yard not the sewer/septic system – full replacement needed
- Septic system is not designed to accommodate additional septic load of detached building – check with city/county planning
- Un-professional (DIY) installation of plumbing (missing traps/vents/etc…) – selective repairs or full replacement needed
The best way to maintain all Detached buildings
- Regularly maintain gutters, downspouts and extension drains
- Maintain the grade at all sides of the home so there is adequate clearance and slope
- Regular dehumidification during rainy/hot/humid months (recommend to set dehumidifier to 55-60%RH)
- Paint every 8 years and stain every 3 years (deck or stained siding)
- Treat for carpenter bees and other wood destroying insects annually or as needed
- Keep shrubs, vines, storage, mulch, and trees away from the building
- Hire professionals for electric and plumbing work- get permits if needed.
Detached buildings add utility and value to a home. Unfortunately corners are cut during their installation and maintenance that significantly shorten their life expectancy. A good home inspector is an invaluable resource for people buying, selling or maintaining detached buildings to help them assess the condition and anticipate repairs and upgrades.
Asheville Detached Building Inspectors
Builder Buddy is your resource for Detached Building Inspections in the Asheville area. We also provide Shed Inspections, Mother-in-law inspections, ADU inspections, Studio Inspections, STR or Short Term Rental Inspections, Tiny Home Inspections, Single-wide trailer inspections, Outbuilding Inspections, Barn inspections, Detached garage inspections, Garage inspections, Detached Building Wood Destroying Insect Inspections (“Pest” Inspections) and more.