Short answer: the wall you share with the next unit is presumed to be a party wall, owned by both of you. You can raise it, repair it and build against it, but the Civil Code sets the terms: you pay for your changes, you can't open a window through it without consent, and you can't dig in a way that takes away your neighbour's support.
A townhouse dispute doesn't need bad intentions to start. It can start with a contractor cutting a chase for new wiring, a second floor that leans on a 100 mm wall, or a septic tank dug a metre from the neighbour's footing. By the time the crack shows up next door, you're arguing about money instead of fixing a wall.
Pick what you're planning. The check lists the Civil Code article, the engineering question and the paperwork that apply, in the order they tend to cause trouble.
Article 659 presumes a party wall "in dividing walls of adjoining buildings up to the point of common elevation", unless a title, an exterior sign or other proof says otherwise. For most townhouses and row houses, that presumption is where you start.
Article 660 lists the exterior signs that point the other way. The ones you'll actually meet in a townhouse are these:
Where a sign exists, the wall is deemed to belong exclusively to the owner it favours. That's worth knowing before you anchor your new roof beams into a wall that the evidence says is your neighbour's.
| Situation | Who pays | Article |
|---|---|---|
| Ordinary repair of the party wall | All owners with the wall in their favour, in proportion to each one's right | 662 |
| You want out of the repair bill | You can renounce part-ownership, except where the wall supports your own building | 662 |
| You demolish your unit | You may renounce part-ownership, but you pay all work needed to keep the demolition from damaging the wall | 663 |
| You raise the wall | You pay the work, any damage even if temporary, upkeep of the new part, and the extra cost of preserving the wall | 664 |
| The wall can't take the extra height | You rebuild it at your expense, taking any extra thickness from your own land | 664 |
| Neighbour later wants to use your raised part | They buy in, paying a proportional share of its value and of the land used | 665 |
Read the second row twice. In a townhouse the dividing wall almost always carries part of your own house, so walking away from the repair cost usually isn't an option.
Article 664 tells you who pays when the wall "cannot bear the increased height". It doesn't tell you whether it can. That's an engineering check, and a 100 mm hollow block wall fails part of it before anyone runs a number.
Most of the country is in Seismic Zone 4 under NSCP 2015 Section 208.4.4.1. The only Zone 2 areas are Palawan (except Busuanga), Sulu and Tawi-Tawi. In Zone 4, Section 707.1.3.1 requires reinforced masonry bearing walls to be at least 150 mm nominal, and the 100 mm exception covers only high-strength clay units, not concrete hollow blocks. So a 100 mm CHB dividing wall is a partition as far as the structural code is concerned. You can't hang a new floor on it and call it done.
Find out what actually carries the existing roof: columns and beams, or the walls. Find out what's under the party wall, because in some row houses one footing serves both units. Adding load to it adds load to your neighbour's foundation too. Our second-floor screening check works through the column and footing side of the same question.
Septic tanks, cisterns and deeper footings are where a townhouse renovation can do real damage next door. Article 684 is blunt: no proprietor shall make excavations that deprive an adjacent building of sufficient lateral or subjacent support. Article 685 voids any agreement allowing excavations that endanger it, and Article 686 extends the protection to buildings erected later.
That means your neighbour's signature doesn't make an unsafe excavation legal. What protects both of you is a shoring and sequencing plan from an engineer before the first shovel goes in.
PD 1096 Section 301 requires a building permit before anyone erects, constructs, alters, repairs, converts or demolishes a building. Every option in the risk check except purely cosmetic interior work falls inside that.
If your townhouse is in a subdivision with a homeowners' association, RA 9904 Section 10 gives the association power to adopt rules and regulations and to regulate the use, maintenance, repair and modification of common areas. Check its construction rules before you mobilise. A stop order from the gate costs more in idle labour than a week of reading.
Articles 659, 660, 662 to 668 and 684 to 686 are quoted from Republic Act 386, the Civil Code. The permit requirement is PD 1096 Section 301. The association's powers are RA 9904 Section 10. The masonry minimum and seismic zone are NSCP 2015 Sections 707.1.3.1 and 208.4.4.1. None of this replaces a lawyer reading your title and deed.
Who owns the wall between two townhouses?
Unless there is a title, an exterior sign or other proof to the contrary, the law presumes it is shared. Article 659 of the Civil Code presumes a party wall in the dividing walls of adjoining buildings up to the point of common elevation. Article 660 lists the signs that point the other way, such as a window in the wall, the wall sitting entirely inside one lot, or the wall carrying the beams, floors and roof of only one of the buildings. Where one of those signs exists, the wall is deemed to belong to the owner it favours.
Can my neighbour open a window in our shared wall?
Not without your consent. Article 667 of the Civil Code says no part-owner may, without the consent of the others, open through the party wall any window or aperture of any kind. Put any consent in writing, because Article 668 counts the period for acquiring an easement of light and view from the time a window is opened through a party wall.
Who pays to repair a party wall?
The owners who have the wall in their favour, in proportion to the right of each, under Article 662. An owner can escape the charge by renouncing part-ownership, but not when the party wall supports a building that belongs to that owner, which is almost always the case with townhouses.
Can I add a second floor to my townhouse?
Possibly, but it is an engineering question before it is a design one. Raising the party wall is allowed at your own expense under Article 664, and you pay for any damage the work causes, even temporary damage. If the wall cannot carry the added height you must rebuild it at your cost, taking any extra thickness from your own land. Separately, NSCP 2015 Section 707.1.3.1 requires reinforced concrete masonry bearing walls in Seismic Zone 4 to be at least 150 mm nominal, so a 100 mm hollow block party wall cannot simply be treated as the support for a new floor.
Can I dig a septic tank or cistern next to the party wall?
Only if the excavation does not take away the support the neighbouring building relies on. Article 684 says no proprietor shall make excavations that deprive an adjacent land or building of sufficient lateral or subjacent support. Article 685 voids any agreement allowing excavations that endanger the adjacent building, so a signed waiver from your neighbour does not protect you.
Do I need a building permit for a townhouse renovation?
Section 301 of PD 1096 requires a building permit before anyone erects, constructs, alters, repairs, converts or demolishes a building. Work on a party wall, a new storey, or excavation near the wall all fall inside that. For purely cosmetic interior work, ask the building official whether a permit is needed before you start.
Statutes and code provisions used in this guide. Links open in a new tab.
This guide explains the rules an engineer works with. It is not legal advice, and who owns a particular wall can turn on the title, the survey and the deed of sale.
A crack in your neighbour's bedroom is a far more expensive conversation than a site visit.
