12 Things to Check When Buying an Old House

Fun fact: 1986 was the average year of construction for the houses bought after 2022.

Older houses have a unique charm that new constructions often lack. They come with historical significance, authentic architectural details, but also a range of hidden issues that buyers sometimes overlook or underestimate.

If you’re considering buying an older home, keep reading, this blog is made for you! Here are 12 things to check when buying an old house.

1. Foundations

A house is built from the ground up, so the inspection should start there as well.

Forget about a DIY inspection and hire an experienced professional who understands the weak points of house foundations in the region you’re interested in and can recognize all potential damage.

These issues aren’t always visible to the naked eye, but an expert who knows where to look can identify them through specific signs, such as:

• Cracked drywall
• Doors and windows that seem misaligned and are harder to open or close
• Broken tiles
• Uneven floors
• Cracks on the exterior walls

In older houses, foundation problems often come from factors like soil shifting over time, inadequate drainage, or poor construction methods, but there is another factor people don’t always think about.

Tree roots.

Over the years, they spread beneath the structure, slowly pushing against the foundation and causing cracks or uneven floors. Certain species, like walnut trees, are particularly invasive in this regard. If you see large trees near a house during a viewing, pay special attention.

2. The Roof

The roof of an old house built in a specific architectural style is often a distinctive feature that adds charm, but it can also become the second largest expense, right after purchasing the house itself.

Roof repair materials alone can cost up to $12,000. That’s why you shouldn’t leave anything to chance! Hire a professional to thoroughly inspect the roof and assess its condition.

Here are some signs that indicate it may need reconstruction or at least a deep cleaning and cosmetic repairs:

• Leaks
• Missing shingles or tiles
• Moss buildup
• Mold traces
• Sagging sections

If you notice any of the signs, consult an expert to determine the amount of damage and work needed to be done, followed by the price of the repair.

3. Plumbing

When viewing an old house, be sure to ask when the plumbing system was installed and when it was last serviced. Before making a final decision, it’s essential to bring in an experienced plumber for a thorough inspection to avoid any hidden issues.

Potential plumbing problems can often be detected through these warning signs:

• Unusual water discoloration
• Inconsistent water pressure
• An unexpectedly high water bill
• Wall stains or damp patches

Installing new rough-in plumbing costs around $4.50 per square foot. For a 2,000-square-foot home, full pipe replacement (including fixtures and labor) can cost from $10,000 to $12,000.

4. Sewer

The sewer system is one of the most overlooked aspects when buying an old house, yet it’s one of the most expensive to repair if problems arise.

Most homebuyers assume that if a house is connected to a municipal sewer system, there’s nothing to worry about, but that’s not entirely true. The homeowner is responsible for the sewer line running from the house to the city connection, and if it’s damaged, clogged, or collapsing, the repairs will come out of your pocket.

Sewer issues in older homes often stem from aging pipes, tree root invasions, or materials like clay or Orangeburg pipes, which were common in mid 20th-century construction but deteriorate over time.

A sewer line inspection, often called a “scope,” involves running a small camera through the pipes to check for blockages, cracks, or collapses. Without it, you could unknowingly inherit a costly problem that only becomes apparent once backups start happening.

Signs of sewer trouble include:

• Foul, sulfur-like odors
• Frequent drain clogs
• Slow drainage throughout the house
• Patches of overly green grass in the yard
• Soft, sunken spots or unexplained puddles outside

The cost of sewer line replacement varies but typically falls between $3,000 and $6,000, but it can depend on factors like location, pipe material, and whether trenchless repair methods can be used. In cases where the sewer line runs under a driveway or other hardscape, costs can be much higher.

While a standard home inspection doesn’t include a sewer check, it’s worth hiring a professional to inspect the line before closing the deal. A simple camera inspection, which usually costs a few hundred dollars, can save you from an unexpected five-figure repair bill down the road.

5. Wires

Old houses often come with outdated electrical systems that weren’t built to handle modern power demands. Decades ago, homes didn’t have high-wattage appliances, computers, and charging stations for multiple devices, so the wiring was designed for lower electrical loads. If the system hasn’t been updated, it may struggle to support even basic household needs today, leading to frequent circuit overloads and potential fire hazards.

Some older homes still have knob-and-tube wiring, a system used in houses built before the 1940s. While not inherently dangerous, it lacks grounding and is incompatible with modern insulation, which can increase the risk of electrical fires. Others may have aluminum wiring, common in homes from the 1960s and 70s, which expands and contracts more than copper, leading to loose connections and overheating.

Signs that an old house may have electrical issues include:

• A persistent burning smell near outlets or breaker panels
• Flickering or dimming lights, especially when multiple appliances are running
• Frequent breaker trips or blown fuses
• Outlets that feel warm to the touch or appear discolored
• Buzzing sounds from outlets or switches
• A switch that vibrates or delivers a mild shock when touched

Replacing an outdated electrical system can be costly. Completely rewiring a home due to deteriorated insulation or unsafe materials can exceed $15,000, while upgrading an overloaded electrical panel to handle modern appliances may cost between $1,300 and $3,000.

If you’re considering buying an older home, an electrical inspection is a must. A licensed electrician can assess whether the wiring is safe, whether the panel needs upgrading, and whether the home meets modern safety codes. 

6. Doors and windows

Doors and windows in old houses often have an aesthetic charm, but they can also be a source of significant heat loss, poor insulation, and security risks.

Many older homes still have their original wooden windows and doors, which, while visually appealing, may have deteriorated over time, allowing drafts, moisture buildup, and even pests to enter.

Single-pane glass, which is common in historic homes, offers little insulation compared to modern double- or triple-pane windows. That’s why winters are colder, and energy bills are higher in homes like these.

Beyond comfort, outdated doors and windows can also pose a security concern. Weak locks, warped frames, or brittle glass can make break-ins easier, especially if the home has never had reinforcements added.

Signs that windows and doors may need repairs or replacements include:

• Cold drafts coming through even when shut
• Difficulty opening or closing due to warping or frame shifting
• Condensation or foggy glass, a sign of a broken window seal
• Dead insects or wings near window sills, indicating gaps for pests
• Creaking or loose locks, reducing home security

While replacing doors and windows can be expensive, it’s often necessary for better insulation, safety, and energy efficiency. A full door replacement, especially for an exterior door with a damaged frame, can range from $2,000 to $4,000. The cost of replacing a window varies significantly depending on materials, with basic vinyl windows starting around $200 to $300, while high-quality wooden or custom windows can cost thousands per unit.

7. Insulation

Many old houses were built before modern insulation standards, making them prone to heat loss in the winter and excessive heat retention in the summer. Poor insulation leads to uncomfortable indoor temperatures, significantly increasing energy bills, as heating and cooling systems must work harder to maintain a stable climate.

Older homes often have little to no insulation in walls, attics, and crawl spaces, or they may still contain outdated materials like sawdust, newspaper, or vermiculite insulation, some of which, like older vermiculite, can contain asbestos. 

And we shouldn’t forget that gaps around doors, windows, and in the foundation can even further contribute to drafts and moisture intrusion.

Signs of poor insulation include:

• Uneven temperatures throughout the house
• Cold floors and walls, even when the heating is on
• High energy bills, especially in extreme weather
• Frequent ice dams on the roof, caused by heat escaping from the attic
• Condensation or mold growth, indicating moisture infiltration

Before purchasing an older home, it’s crucial to check the insulation levels in areas like the attic, exterior walls, and basement. In some cases, adding weather stripping, sealing gaps, or installing storm windows can provide noticeable improvements without requiring a full insulation overhaul.

Blown-in insulation for an attic can cost $1,500 to $3,000, while wall insulation retrofitting can range from $3,000 to $8,000, depending on the method used. However, the long-term savings on heating and cooling bills often make it worthwhile.

8. Hidden Mold

Mold is one of the most overlooked yet serious problems in older homes. Unlike visible mold, which grows on walls and ceilings, hidden mold can lurk behind drywall, under flooring, or inside HVAC systems, causing damage long before it becomes noticeable.

The biggest issue with hidden mold is that it thrives in damp, poorly ventilated spaces, which are common in older houses with outdated insulation, leaky roofs, or past water damage.

If not treated in the right way, it can weaken wooden structures, damage drywall, and create persistent odors. More importantly, mold spores can lead to respiratory issues, allergies, and other health problems, particularly for individuals with asthma or weakened immune systems.

Warning signs of hidden mold:

• Musty or earthy odors, even if no mold is visible
• Discolored or bubbling paint and wallpaper
• Warped or soft drywall, which may indicate moisture buildup
• Unexplained allergic reactions, such as coughing, sneezing, or skin irritation
• Dark stains on ceilings or walls, especially near windows, pipes, or in basements

A visual inspection may not be enough to detect mold behind walls or under flooring. A professional mold inspection, which includes moisture readings and air quality tests, can identify mold even when it’s not visible. If mold is found, remediation costs can range from $1,500 to over $6,000, depending on the severity and affected area.

Before purchasing an older home, don’t forget to check for past water damage, leaks, or signs of poor ventilation, as these increase the risk of hidden mold.

9. Rodents

Older homes often have small gaps, cracks, and hidden entry points that make them an easy target for rodents.

Mice and rats can squeeze through openings as small as a dime, and once inside, they can cause significant damage by gnawing on electrical wiring, insulation, and even wooden structures. More importantly, they bring serious health risks, as they can carry bacteria and viruses, contaminating food and surfaces.

Signs of a rodent infestation:

• Droppings in cabinets, pantries, or along baseboards
• Scratching noises in walls, ceilings, or attics, especially at night
• Gnawed wires, furniture, or food packaging
• Musty or ammonia-like odors, particularly in enclosed spaces
• Nest materials, such as shredded paper or fabric

If rodents have made their way into the home, removing them and sealing entry points should be a top priority. Professional pest control services can cost anywhere from $200 to $600, depending on the severity of the infestation. If the problem is extensive, additional repairs may be needed to fix damaged insulation, wiring, or wall cavities.

10. Toxic Materials and Gases

In the past, many houses were built using materials that are now known to be hazardous. Asbestos, once widely used for insulation and fire resistance, was later linked to severe health risks, including lung disease and cancer.

Similarly, buildings constructed before 1978 often contained lead-based paint, which poses serious dangers, especially to children, as lead exposure can cause developmental issues and neurological damage.

Another hidden danger was radon, a naturally occurring radioactive gas that can accumulate in poorly ventilated homes, increasing the risk of lung cancer. And even some older plumbing systems were made with lead pipes, which can contaminate drinking water over time.

Signs of Toxic Material Presence:

• Peeling or chipping paint, especially in homes built before 1978 (potential lead exposure)
• Persistent coughing, headaches, or respiratory issues (could indicate asbestos or radon exposure)
• Unexplained fatigue or nausea, which may be linked to high radon levels
• Metallic taste in drinking water, possibly caused by lead contamination
• Dusty or crumbling insulation in attics or basements, which may contain asbestos

11. HVAC

Many older houses still use inefficient furnaces, radiators, or lack central air conditioning. An outdated heating, ventilation, and air conditioning (HVAC) system in an old home can lead to high energy bills, poor temperature regulation, and even safety risks.

Signs of HVAC issues can be:

• Old or inefficient heating systems that drive up costs
• Lack of central air, requiring costly ductwork installation
• Leaky or poorly insulated ducts, reducing efficiency
• Clogged filters or poor maintenance, leading to weak airflow
• Carbon monoxide risks from outdated furnaces

Before buying an older home, check the age of the HVAC system, as units over 15–20 years old may need replacing, which can cost between $5,000 and $12,000. Inspect the ductwork condition for leaks, dust buildup, or poor insulation, as these issues can reduce efficiency.

Pay attention to ventilation quality, since blocked vents may lead to moisture problems and mold growth. Additionally, reviewing past utility bills can help assess the system’s energy efficiency and potential heating and cooling costs.

Regular air duct cleaning is probably the most important part for maintaining the high indoor air quality and HVAC performance.

12. Historic value

Owning a historic home comes with charm, character, and a deep connection to the past, but it also comes with strict regulations and potential limitations on renovations.

If a home is officially designated as historic or located within a historic district, you may face restrictions on exterior modifications, additions, and even the smallest interior changes.

A property typically qualifies as historic if it is at least 50 years old and meets one of the following criteria:

• Connected to a significant historical event or figure
• Represents a distinct architectural style or craftsmanship from a specific era
• Holds historical or cultural significance within its community

Because historic homes are meant to be preserved, they are often subject to local, state, or federal regulations that require homeowners to obtain permits for major changes.

Depending on the home’s designation, you may be prohibited from altering the façade, replacing original materials with modern alternatives, or changing structural elements like windows, doors, and roofing. In many cases, repairs must be completed using historically accurate materials and techniques, which can drive up renovation costs significantly.

If you’re considering purchasing a historic home, be prepared for extra costs and bureaucratic hurdles. Repairs and renovations often require specialized craftsmanship, permits can slow down the process, and there may be limitations on expanding or modernizing the home. Before buying, research local historic preservation rules and check with the State Historic Preservation Office (SHPO) to understand what restrictions apply.

Buying an old house can be a rewarding investment, but hidden issues can lead to unexpected and costly repairs. A thorough inspection and proactive approach will help you identify potential problems early, and be sure that your home is both safe and valuable.